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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/macros/" rel="canonical"><link href=../ordered_map/ rel=prev><link href=json_assert/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.6"><title>Overview - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.484c7ddc.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-search data-md-component=sLine truncated
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# Macros
Some aspects of the library can be configured by defining preprocessor macros **before** including the `json.hpp` header. See also the [macro overview page](https://json.nlohmann.me/features/macros/index.md).
## Runtime assertions
- [**JSON_ASSERT(x)**](https://json.nlohmann.me/api/macros/json_assert/index.md) - control behavior of runtime assertions
## Exceptions
- [**JSON_CATCH_USER(exception)**\
**JSON_THROW_USER(exception)**\
**JSON_TRY_USER**](https://json.nlohmann.me/api/macros/json_throw_user/index.md) - control exceptions
- [**JSON_DIAGNOSTICS**](https://json.nlohmann.me/api/macros/json_diagnostics/index.md) - control extended diagnostics
- [**JSON_DIAGNOSTIC_POSITIONS**](https://json.nlohmann.me/api/macros/json_diagnostic_positions/index.md) - access positions of elements
- [**JSON_NOEXCEPTION**](https://json.nlohmann.me/api/macros/json_noexception/index.md) - switch off exceptions
## Language support
- [**JSON_HAS_CPP_11**\
**JSON_HAS_CPP_14**\
**JSON_HAS_CPP_17**\
**JSON_HAS_CPP_20**](https://json.nlohmann.me/api/macros/json_has_cpp_11/index.md) - set supported C++ standard
- [**JSON_HAS_FILESYSTEM**\
**JSON_HAS_EXPERIMENTAL_FILESYSTEM**](https://json.nlohmann.me/api/macros/json_has_filesystem/index.md) - control `std::filesystem` support
- [**JSON_HAS_RANGES**](https://json.nlohmann.me/api/macros/json_has_ranges/index.md) - control `std::ranges` support
- [**JSON_HAS_STD_FORMAT**](https://json.nlohmann.me/api/macros/json_has_std_format/index.md) - control `std::format`/`std::formatter` support
- [**JSON_HAS_THREE_WAY_COMPARISON**](https://json.nlohmann.me/api/macros/json_has_three_way_comparison/index.md) - control 3-way comparison support
- [**JSON_NO_IO**](https://json.nlohmann.me/api/macros/json_no_io/index.md) - switch off functions relying on certain C++ I/O headers
- [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](https://json.nlohmann.me/api/macros/json_skip_unsupported_compiler_check/index.md) - do not warn about unsupported compilers
- [**JSON_USE_GLOBAL_UDLS**](https://json.nlohmann.me/api/macros/json_use_global_udls/index.md) - place user-defined string literals (UDLs) into the global namespace
## Library version
- [**JSON_SKIP_LIBRARY_VERSION_CHECK**](https://json.nlohmann.me/api/macros/json_skip_library_version_check/index.md) - skip library version check
- [**NLOHMANN_JSON_VERSION_MAJOR**\
**NLOHMANN_JSON_VERSION_MINOR**\
**NLOHMANN_JSON_VERSION_PATCH**](https://json.nlohmann.me/api/macros/nlohmann_json_version_major/index.md)
- library version information
## Library namespace
- [**NLOHMANN_JSON_NAMESPACE**](https://json.nlohmann.me/api/macros/nlohmann_json_namespace/index.md) - full name of the `nlohmann` namespace
- [**NLOHMANN_JSON_NAMESPACE_BEGIN**\
**NLOHMANN_JSON_NAMESPACE_END**](https://json.nlohmann.me/api/macros/nlohmann_json_namespace_begin/index.md) - open and close the library namespace
- [**NLOHMANN_JSON_NAMESPACE_NO_VERSION**](https://json.nlohmann.me/api/macros/nlohmann_json_namespace_no_version/index.md) - disable the version component of the inline namespace
## Type conversions
- [**JSON_BRACE_INIT_COPY_SEMANTICS**](https://json.nlohmann.me/api/macros/json_brace_init_copy_semantics/index.md) - opt in to copy/move semantics for single-element brace initialization
- [**JSON_DISABLE_ENUM_SERIALIZATION**](https://json.nlohmann.me/api/macros/json_disable_enum_serialization/index.md) - switch off default serialization/deserialization functions for enums
- [**JSON_USE_IMPLICIT_CONVERSIONS**](https://json.nlohmann.me/api/macros/json_use_implicit_conversions/index.md) - control implicit conversions
## Comparison behavior
- [**JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON**](https://json.nlohmann.me/api/macros/json_use_legacy_discarded_value_comparison/index.md) - control comparison of discarded values
## Serialization/deserialization macros
### Enums
- [**NLOHMANN_JSON_SERIALIZE_ENUM**](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/index.md) - serialize/deserialize an enum
- [**NLOHMANN_JSON_SERIALIZE_ENUM_STRICT**](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum_strict/index.md) - serialize/deserialize an enum with exceptions
### Classes and structs
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE**](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) - serialize/deserialize a non-derived class with private members
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT**](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) - serialize/deserialize a non-derived class with private members; uses default values
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE**](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) - serialize a non-derived class with private members
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE**](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md) - serialize/deserialize a non-derived class
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT**](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md) - serialize/deserialize a non-derived class; uses default values
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE**](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md) - serialize a non-derived class
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE**](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) - serialize/deserialize a derived class with private members
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT**](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) - serialize/deserialize a derived class with private members; uses default values
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE**](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) - serialize a derived class with private members
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE**](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) - serialize/deserialize a derived class
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT**](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) - serialize/deserialize a derived class; uses default values
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE**](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) - serialize a derived class
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a non-derived class with private members; uses custom names
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a non-derived class with private members; uses default values; uses custom names
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize a non-derived class with private members; uses custom names
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a non-derived class; uses custom names
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a non-derived class; uses default values; uses custom names
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize a non-derived class; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a derived class with private members; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a derived class with private members; uses default values; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize a derived class with private members; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a derived class; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize/deserialize a derived class; uses default values; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](https://json.nlohmann.me/api/macros/nlohmann_define_type_with_names/index.md) - serialize a derived class; uses custom names
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# JSON_ASSERT
```cpp
#define JSON_ASSERT(x) /* value */
```
This macro controls which code is executed for [runtime assertions](../../features/assertions.md) of the library.
## Parameters
`x` (in)
: expression of a scalar type
## Default definition
The default value is [`#!cpp assert(x)`](https://en.cppreference.com/w/cpp/error/assert).
```cpp
#define JSON_ASSERT(x) assert(x)
```
Therefore, assertions can be switched off by defining `NDEBUG`.
## Notes
- The library uses numerous assertions to guarantee invariants and to abort in case of otherwise undefined behavior
(e.g., when calling [operator[]](../basic_json/operator%5B%5D.md) with a missing object key on a `const` object). See
page [runtime assertions](../../features/assertions.md) for more information.
- Defining the macro to code that does not call `std::abort` may leave the library in an undefined state.
- The macro is undefined outside the library.
## Examples
??? example "Example 1: default behavior"
The following code will trigger an assertion at runtime:
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
const json j = {{"key", "value"}};
auto v = j["missing"];
}
```
Output:
```
Assertion failed: (m_value.object->find(key) != m_value.object->end()), function operator[], file json.hpp, line 2144.
```
??? example "Example 2: user-defined behavior"
The assertion reporting can be changed by defining `JSON_ASSERT(x)` differently.
```cpp
#include <cstdio>
#include <cstdlib>
#define JSON_ASSERT(x) if(!(x)){fprintf(stderr, "assertion error in %s\n", __FUNCTION__); std::abort();}
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
const json j = {{"key", "value"}};
auto v = j["missing"];
}
```
Output:
```
assertion error in operator[]
```
## See also
- [Runtime Assertions](../../features/assertions.md) - overview documentation
## Version history
- Added in version 3.9.0.
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<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>[</span><span class=s>&quot;missing&quot;</span><span class=p>];</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code>assertion error in operator[]
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/assertions/ >Runtime Assertions</a> - overview documentation</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/assertions/ >Runtime Assertions</a> - overview documentation</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+85
View File
@@ -0,0 +1,85 @@
# JSON_ASSERT
```
#define JSON_ASSERT(x) /* value */
```
This macro controls which code is executed for [runtime assertions](https://json.nlohmann.me/features/assertions/index.md) of the library.
## Parameters
`x` (in) : expression of a scalar type
## Default definition
The default value is [`assert(x)`](https://en.cppreference.com/w/cpp/error/assert).
```
#define JSON_ASSERT(x) assert(x)
```
Therefore, assertions can be switched off by defining `NDEBUG`.
## Notes
- The library uses numerous assertions to guarantee invariants and to abort in case of otherwise undefined behavior (e.g., when calling [operator[]](https://json.nlohmann.me/api/basic_json/operator%5B%5D/index.md) with a missing object key on a `const` object). See page [runtime assertions](https://json.nlohmann.me/features/assertions/index.md) for more information.
- Defining the macro to code that does not call `std::abort` may leave the library in an undefined state.
- The macro is undefined outside the library.
## Examples
Example 1: default behavior
The following code will trigger an assertion at runtime:
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
const json j = {{"key", "value"}};
auto v = j["missing"];
}
```
Output:
```
Assertion failed: (m_value.object->find(key) != m_value.object->end()), function operator[], file json.hpp, line 2144.
```
Example 2: user-defined behavior
The assertion reporting can be changed by defining `JSON_ASSERT(x)` differently.
```
#include <cstdio>
#include <cstdlib>
#define JSON_ASSERT(x) if(!(x)){fprintf(stderr, "assertion error in %s\n", __FUNCTION__); std::abort();}
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
const json j = {{"key", "value"}};
auto v = j["missing"];
}
```
Output:
```
assertion error in operator[]
```
## See also
- [Runtime Assertions](https://json.nlohmann.me/features/assertions/index.md) - overview documentation
## Version history
- Added in version 3.9.0.
@@ -0,0 +1,95 @@
# JSON_BRACE_INIT_COPY_SEMANTICS
```cpp
#define JSON_BRACE_INIT_COPY_SEMANTICS /* value */
```
When defined to `1`, single-element brace initialization of a `basic_json` value is treated as a copy/move of the
element rather than wrapping it in a single-element array.
## Default definition
The default value is `0` (disabled — existing behavior is preserved).
```cpp
#define JSON_BRACE_INIT_COPY_SEMANTICS 0
```
## Notes
!!! note "Background"
C++ always prefers the `initializer_list` constructor over the copy/move constructor for brace initialization. This
means that code like
```cpp
json obj = {{"key", "value"}};
json j{obj};
```
creates a single-element **array** `[{"key":"value"}]` instead of a copy of `obj`. This behavior is
compiler-dependent for older compilers (GCC wrapped, Clang did not), but starting from Clang 20, both compilers
behave the same way.
Enabling this macro opts into copy/move semantics for this case
(see [#5074](https://github.com/nlohmann/json/issues/5074)).
!!! warning "Opt-in only"
This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no effect.
!!! tip "Workaround without the macro"
To explicitly create a single-element array without enabling this macro, use `json::array()`:
```cpp
json j = json::array({obj}); // always creates [obj]
```
## Examples
??? example "Default behavior (macro not defined)"
Without the macro, single-element brace initialization wraps the value in an array:
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
json obj = {{"key", "value"}};
json j{obj};
// j is [{"key":"value"}] -- single-element array, NOT a copy of obj
}
```
??? example "Opt-in copy semantics (macro defined to 1)"
With the macro, single-element brace initialization copies/moves the value:
```cpp
#define JSON_BRACE_INIT_COPY_SEMANTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
json obj = {{"key", "value"}};
json j{obj};
// j is {"key":"value"} -- copy of obj
}
```
## See also
- [FAQ: Brace initialization yields arrays](../../home/faq.md#brace-initialization-yields-arrays)
- [**basic_json(initializer_list_t)**](../basic_json/basic_json.md) - the affected constructor
## Version history
- Added in version 3.12.x.
@@ -26,4 +26,4 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>{</span><span class=n>obj</span><span class=p>};</span>
<span class=w> </span><span class=c1>// j is {&quot;key&quot;:&quot;value&quot;} -- copy of obj</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/faq/#brace-initialization-yields-arrays><abbr title="Frequently Asked Questions">FAQ</abbr>: Brace initialization yields arrays</a></li> <li><a href=../../basic_json/basic_json/ ><strong>basic_json(initializer_list_t)</strong></a> - the affected constructor</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.x.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/faq/#brace-initialization-yields-arrays><abbr title="Frequently Asked Questions">FAQ</abbr>: Brace initialization yields arrays</a></li> <li><a href=../../basic_json/basic_json/ ><strong>basic_json(initializer_list_t)</strong></a> - the affected constructor</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.x.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,90 @@
# JSON_BRACE_INIT_COPY_SEMANTICS
```
#define JSON_BRACE_INIT_COPY_SEMANTICS /* value */
```
When defined to `1`, single-element brace initialization of a `basic_json` value is treated as a copy/move of the element rather than wrapping it in a single-element array.
## Default definition
The default value is `0` (disabled — existing behavior is preserved).
```
#define JSON_BRACE_INIT_COPY_SEMANTICS 0
```
## Notes
Background
C++ always prefers the `initializer_list` constructor over the copy/move constructor for brace initialization. This means that code like
```
json obj = {{"key", "value"}};
json j{obj};
```
creates a single-element **array** `[{"key":"value"}]` instead of a copy of `obj`. This behavior is compiler-dependent for older compilers (GCC wrapped, Clang did not), but starting from Clang 20, both compilers behave the same way.
Enabling this macro opts into copy/move semantics for this case (see [#5074](https://github.com/nlohmann/json/issues/5074)).
Opt-in only
This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no effect.
Workaround without the macro
To explicitly create a single-element array without enabling this macro, use `json::array()`:
```
json j = json::array({obj}); // always creates [obj]
```
## Examples
Default behavior (macro not defined)
Without the macro, single-element brace initialization wraps the value in an array:
```
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
json obj = {{"key", "value"}};
json j{obj};
// j is [{"key":"value"}] -- single-element array, NOT a copy of obj
}
```
Opt-in copy semantics (macro defined to 1)
With the macro, single-element brace initialization copies/moves the value:
```
#define JSON_BRACE_INIT_COPY_SEMANTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
json obj = {{"key", "value"}};
json j{obj};
// j is {"key":"value"} -- copy of obj
}
```
## See also
- [FAQ: Brace initialization yields arrays](https://json.nlohmann.me/home/faq/#brace-initialization-yields-arrays)
- [**basic_json(initializer_list_t)**](https://json.nlohmann.me/api/basic_json/basic_json/index.md) - the affected constructor
## Version history
- Added in version 3.12.x.
+119
View File
@@ -0,0 +1,119 @@
# JSON_DIAGNOSTIC_POSITIONS
```cpp
#define JSON_DIAGNOSTIC_POSITIONS /* value */
```
This macro enables position diagnostics for generated JSON objects.
When enabled, two new member functions [`start_pos()`](../basic_json/start_pos.md) and
[`end_pos()`](../basic_json/end_pos.md) are added to [`basic_json`](../basic_json/index.md) values. If the value was
created by calling the[`parse`](../basic_json/parse.md) function, then these functions allow querying the byte positions
of the value in the input it was parsed from. In case the value was constructed by other means, `std::string::npos` is
returned.
[`start_pos()`](../basic_json/start_pos.md) returns the position of the first character of a given value in the original
JSON string, while [`end_pos()`](../basic_json/end_pos.md) returns the position of the character _following_ the last
character. For objects and arrays, the first and last characters correspond to the opening or closing braces/brackets,
respectively. For primitive values, the first and last character represents the opening and closing quotes (strings) or
the first and last character of the field's numerical or predefined value (`true`, `false`, `null`), respectively.
| JSON type | return value [`start_pos()`](../basic_json/start_pos.md) | return value [`end_pos()`](../basic_json/end_pos.md) |
|-----------|----------------------------------------------------------|------------------------------------------------------|
| object | position of the opening `{` | position after the closing `}` |
| array | position of the opening `[` | position after the closing `]` |
| string | position of the opening `"` | position after the closing `"` |
| number | position of the first character | position after the last character |
| boolean | position of `t` for `true` and `f` for `false` | position after `e` |
| null | position of `n` | position after `l` |
Given the above, [`end_pos()`](../basic_json/end_pos.md)` - `[`start_pos()`](../basic_json/start_pos.md) for a JSON
value provides the length of the parsed JSON string for that value, including the opening or closing braces, brackets,
or quotes.
Note that enabling this macro increases the size of every JSON value by two `std::size_t` fields and adds slight runtime
overhead to parsing, copying JSON value objects, and the generation of error messages for exceptions. It also causes
these values to be reported in those error messages.
## Default definition
The default value is `0` (position diagnostics are switched off).
```cpp
#define JSON_DIAGNOSTIC_POSITIONS 0
```
When the macro is not defined, the library will define it to its default value.
## Notes
!!! note "CMake option"
Diagnostic positions can also be controlled with the CMake option
[`JSON_Diagnostic_Positions`](../../integration/cmake.md#json_diagnostic_positions) (`OFF` by default)
which defines `JSON_DIAGNOSTIC_POSITIONS` accordingly.
!!! note "Availability"
Diagnostic positions are only available if the value was created by the [`parse`](../basic_json/parse.md) function.
The [`sax_parse`](../basic_json/sax_parse.md) function or all other means to create a JSON value **do not** set the
diagnostic positions and [`start_pos()`](../basic_json/start_pos.md) and [`end_pos()`](../basic_json/end_pos.md)
will only return `std::string::npos` for these values.
!!! warning "Invalidation"
The returned positions are only valid as long as the JSON value is not changed. The positions are *not* updated
when the JSON value is changed.
## Examples
??? example "Example: retrieving positions"
```cpp
--8<-- "examples/diagnostic_positions.cpp"
```
Output:
```
--8<-- "examples/diagnostic_positions.output"
```
The output shows the start/end positions of all the objects and fields in the JSON string.
??? example "Example 2: using only diagnostic positions in exceptions"
```cpp
--8<-- "examples/diagnostic_positions_exception.cpp"
```
Output:
```
--8<-- "examples/diagnostic_positions_exception.output"
```
The output shows the exception with start/end positions only.
??? example "Example 3: using extended diagnostics with positions enabled in exceptions"
```cpp
--8<-- "examples/diagnostics_extended_positions.cpp"
```
Output:
```
--8<-- "examples/diagnostics_extended_positions.output"
```
The output shows the exception with diagnostic path info and start/end positions.
## See also
- [:simple-cmake: JSON_Diagnostic_Positions](../../integration/cmake.md#json_diagnostic_positions) - CMake option to control the macro
- [JSON_DIAGNOSTICS](json_diagnostics.md) - macro to control extended diagnostics
## Version history
- Added in version 3.12.0.
@@ -165,4 +165,4 @@ Parsed string:
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code>[json.exception.type_error.302] (/address/housenumber) (bytes 92-95) type must be number, but is string
</code></pre></div> <div class=codehilite><pre><span></span><code>The output shows the exception with diagnostic path info and start/end positions.
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_diagnostic_positions><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_Diagnostic_Positions</a> - CMake option to control the macro</li> <li><a href=../json_diagnostics/ >JSON_DIAGNOSTICS</a> - macro to control extended diagnostics</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_diagnostic_positions><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_Diagnostic_Positions</a> - CMake option to control the macro</li> <li><a href=../json_diagnostics/ >JSON_DIAGNOSTICS</a> - macro to control extended diagnostics</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,262 @@
# JSON_DIAGNOSTIC_POSITIONS
```
#define JSON_DIAGNOSTIC_POSITIONS /* value */
```
This macro enables position diagnostics for generated JSON objects.
When enabled, two new member functions [`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md) and [`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md) are added to [`basic_json`](https://json.nlohmann.me/api/basic_json/index.md) values. If the value was created by calling the[`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) function, then these functions allow querying the byte positions of the value in the input it was parsed from. In case the value was constructed by other means, `std::string::npos` is returned.
[`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md) returns the position of the first character of a given value in the original JSON string, while [`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md) returns the position of the character *following* the last character. For objects and arrays, the first and last characters correspond to the opening or closing braces/brackets, respectively. For primitive values, the first and last character represents the opening and closing quotes (strings) or the first and last character of the field's numerical or predefined value (`true`, `false`, `null`), respectively.
| JSON type | return value [`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md) | return value [`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md) |
| --------- | ---------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------ |
| object | position of the opening `{` | position after the closing `}` |
| array | position of the opening `[` | position after the closing `]` |
| string | position of the opening `"` | position after the closing `"` |
| number | position of the first character | position after the last character |
| boolean | position of `t` for `true` and `f` for `false` | position after `e` |
| null | position of `n` | position after `l` |
Given the above, [`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md)`-`[`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md) for a JSON value provides the length of the parsed JSON string for that value, including the opening or closing braces, brackets, or quotes.
Note that enabling this macro increases the size of every JSON value by two `std::size_t` fields and adds slight runtime overhead to parsing, copying JSON value objects, and the generation of error messages for exceptions. It also causes these values to be reported in those error messages.
## Default definition
The default value is `0` (position diagnostics are switched off).
```
#define JSON_DIAGNOSTIC_POSITIONS 0
```
When the macro is not defined, the library will define it to its default value.
## Notes
CMake option
Diagnostic positions can also be controlled with the CMake option [`JSON_Diagnostic_Positions`](https://json.nlohmann.me/integration/cmake/#json_diagnostic_positions) (`OFF` by default) which defines `JSON_DIAGNOSTIC_POSITIONS` accordingly.
Availability
Diagnostic positions are only available if the value was created by the [`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) function. The [`sax_parse`](https://json.nlohmann.me/api/basic_json/sax_parse/index.md) function or all other means to create a JSON value **do not** set the diagnostic positions and [`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md) and [`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md) will only return `std::string::npos` for these values.
Invalidation
The returned positions are only valid as long as the JSON value is not changed. The positions are *not* updated when the JSON value is changed.
## Examples
Example: retrieving positions
```
#include <iostream>
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
std::string json_string = R"(
{
"address": {
"street": "Fake Street",
"housenumber": 1
}
}
)";
json j = json::parse(json_string);
std::cout << "Root diagnostic positions: \n";
std::cout << "\tstart_pos: " << j.start_pos() << '\n';
std::cout << "\tend_pos:" << j.end_pos() << "\n";
std::cout << "Original string: \n";
std::cout << "{\n \"address\": {\n \"street\": \"Fake Street\",\n \"housenumber\": 1\n }\n }" << "\n";
std::cout << "Parsed string: \n";
std::cout << json_string.substr(j.start_pos(), j.end_pos() - j.start_pos()) << "\n\n";
std::cout << "address diagnostic positions: \n";
std::cout << "\tstart_pos:" << j["address"].start_pos() << '\n';
std::cout << "\tend_pos:" << j["address"].end_pos() << "\n\n";
std::cout << "Original string: \n";
std::cout << "{ \"street\": \"Fake Street\",\n \"housenumber\": 1\n }" << "\n";
std::cout << "Parsed string: \n";
std::cout << json_string.substr(j["address"].start_pos(), j["address"].end_pos() - j["address"].start_pos()) << "\n\n";
std::cout << "street diagnostic positions: \n";
std::cout << "\tstart_pos:" << j["address"]["street"].start_pos() << '\n';
std::cout << "\tend_pos:" << j["address"]["street"].end_pos() << "\n\n";
std::cout << "Original string: \n";
std::cout << "\"Fake Street\"" << "\n";
std::cout << "Parsed string: \n";
std::cout << json_string.substr(j["address"]["street"].start_pos(), j["address"]["street"].end_pos() - j["address"]["street"].start_pos()) << "\n\n";
std::cout << "housenumber diagnostic positions: \n";
std::cout << "\tstart_pos:" << j["address"]["housenumber"].start_pos() << '\n';
std::cout << "\tend_pos:" << j["address"]["housenumber"].end_pos() << "\n\n";
std::cout << "Original string: \n";
std::cout << "1" << "\n";
std::cout << "Parsed string: \n";
std::cout << json_string.substr(j["address"]["housenumber"].start_pos(), j["address"]["housenumber"].end_pos() - j["address"]["housenumber"].start_pos()) << "\n\n";
}
```
Output:
```
Root diagnostic positions:
start_pos: 5
end_pos:109
Original string:
{
"address": {
"street": "Fake Street",
"housenumber": 1
}
}
Parsed string:
{
"address": {
"street": "Fake Street",
"housenumber": 1
}
}
address diagnostic positions:
start_pos:26
end_pos:103
Original string:
{ "street": "Fake Street",
"housenumber": 1
}
Parsed string:
{
"street": "Fake Street",
"housenumber": 1
}
street diagnostic positions:
start_pos:50
end_pos:63
Original string:
"Fake Street"
Parsed string:
"Fake Street"
housenumber diagnostic positions:
start_pos:92
end_pos:93
Original string:
1
Parsed string:
1
```
The output shows the start/end positions of all the objects and fields in the JSON string.
Example 2: using only diagnostic positions in exceptions
```
#include <iostream>
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
{
//Invalid json string - housenumber type must be int instead of string
const std::string json_invalid_string = R"(
{
"address": {
"street": "Fake Street",
"housenumber": "1"
}
}
)";
json j = json::parse(json_invalid_string);
try
{
int housenumber = j["address"]["housenumber"];
std::cout << housenumber;
}
catch (const json::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
[json.exception.type_error.302] (bytes 92-95) type must be number, but is string
```
```
The output shows the exception with start/end positions only.
```
Example 3: using extended diagnostics with positions enabled in exceptions
```
#include <iostream>
#define JSON_DIAGNOSTICS 1
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
{
//Invalid json string - housenumber type must be int instead of string
const std::string json_invalid_string = R"(
{
"address": {
"street": "Fake Street",
"housenumber": "1"
}
}
)";
json j = json::parse(json_invalid_string);
try
{
int housenumber = j["address"]["housenumber"];
std::cout << housenumber;
}
catch (const json::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
[json.exception.type_error.302] (/address/housenumber) (bytes 92-95) type must be number, but is string
```
```
The output shows the exception with diagnostic path info and start/end positions.
```
## See also
- [JSON_Diagnostic_Positions](https://json.nlohmann.me/integration/cmake/#json_diagnostic_positions) - CMake option to control the macro
- [JSON_DIAGNOSTICS](https://json.nlohmann.me/api/macros/json_diagnostics/index.md) - macro to control extended diagnostics
## Version history
- Added in version 3.12.0.
+94
View File
@@ -0,0 +1,94 @@
# JSON_DIAGNOSTICS
```cpp
#define JSON_DIAGNOSTICS /* value */
```
This macro enables [extended diagnostics for exception messages](../../home/exceptions.md#extended-diagnostic-messages).
Possible values are `1` to enable or `0` to disable (default).
When enabled, exception messages contain a [JSON Pointer](../json_pointer/json_pointer.md) to the JSON value that
triggered the exception. Note that enabling this macro increases the size of every JSON value by one pointer and adds
some runtime overhead.
## Default definition
The default value is `0` (extended diagnostics are switched off).
```cpp
#define JSON_DIAGNOSTICS 0
```
When the macro is not defined, the library will define it to its default value.
## Notes
!!! note "ABI compatibility"
As of version 3.11.0, this macro is no longer required to be defined consistently throughout a codebase to avoid
One Definition Rule (ODR) violations, as the value of this macro is encoded in the namespace, resulting in distinct
symbol names.
This allows different parts of a codebase to use different versions or configurations of this library without
causing improper behavior.
Where possible, it is still recommended that all code define this the same way for maximum interoperability.
!!! hint "CMake option"
Diagnostic messages can also be controlled with the CMake option
[`JSON_Diagnostics`](../../integration/cmake.md#json_diagnostics) (`OFF` by default)
which defines `JSON_DIAGNOSTICS` accordingly.
## Examples
??? example "Example 1: default behavior"
```cpp
--8<-- "examples/diagnostics_standard.cpp"
```
Output:
```
--8<-- "examples/diagnostics_standard.output"
```
This exception can be hard to debug if storing the value `#!c "12"` and accessing it is further apart.
??? example "Example 2: extended diagnostic messages"
```cpp
--8<-- "examples/diagnostics_extended.cpp"
```
Output:
```
--8<-- "examples/diagnostics_extended.output"
```
Now the exception message contains a JSON Pointer `/address/housenumber` that indicates which value has the wrong type.
??? example "Example 3: using only diagnostic positions in exceptions"
```cpp
--8<-- "examples/diagnostic_positions_exception.cpp"
```
Output:
```
--8<-- "examples/diagnostic_positions_exception.output"
```
The output shows the exception with start/end positions only.
## See also
- [:simple-cmake: JSON_Diagnostics](../../integration/cmake.md#json_diagnostics) - CMake option to control the macro
- [JSON_DIAGNOSTIC_POSITIONS](json_diagnostic_positions.md) - macro to access positions of elements
## Version history
- Added in version 3.10.0.
- As of version 3.11.0, the definition is allowed to vary between translation units.
+1 -1
View File
@@ -75,4 +75,4 @@
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <p><div class=highlight><pre><span></span><code>[json.exception.type_error.302] (bytes 92-95) type must be number, but is string
</code></pre></div> The output shows the exception with start/end positions only.</p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_diagnostics><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_Diagnostics</a> - CMake option to control the macro</li> <li><a href=../json_diagnostic_positions/ >JSON_DIAGNOSTIC_POSITIONS</a> - macro to access positions of elements</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.0.</li> <li>As of version 3.11.0, the definition is allowed to vary between translation units.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> The output shows the exception with start/end positions only.</p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_diagnostics><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_Diagnostics</a> - CMake option to control the macro</li> <li><a href=../json_diagnostic_positions/ >JSON_DIAGNOSTIC_POSITIONS</a> - macro to access positions of elements</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.0.</li> <li>As of version 3.11.0, the definition is allowed to vary between translation units.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+156
View File
@@ -0,0 +1,156 @@
# JSON_DIAGNOSTICS
```
#define JSON_DIAGNOSTICS /* value */
```
This macro enables [extended diagnostics for exception messages](https://json.nlohmann.me/home/exceptions/#extended-diagnostic-messages). Possible values are `1` to enable or `0` to disable (default).
When enabled, exception messages contain a [JSON Pointer](https://json.nlohmann.me/api/json_pointer/json_pointer/index.md) to the JSON value that triggered the exception. Note that enabling this macro increases the size of every JSON value by one pointer and adds some runtime overhead.
## Default definition
The default value is `0` (extended diagnostics are switched off).
```
#define JSON_DIAGNOSTICS 0
```
When the macro is not defined, the library will define it to its default value.
## Notes
ABI compatibility
As of version 3.11.0, this macro is no longer required to be defined consistently throughout a codebase to avoid One Definition Rule (ODR) violations, as the value of this macro is encoded in the namespace, resulting in distinct symbol names.
This allows different parts of a codebase to use different versions or configurations of this library without causing improper behavior.
Where possible, it is still recommended that all code define this the same way for maximum interoperability.
CMake option
Diagnostic messages can also be controlled with the CMake option [`JSON_Diagnostics`](https://json.nlohmann.me/integration/cmake/#json_diagnostics) (`OFF` by default) which defines `JSON_DIAGNOSTICS` accordingly.
## Examples
Example 1: default behavior
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
json j;
j["address"]["street"] = "Fake Street";
j["address"]["housenumber"] = "12";
try
{
int housenumber = j["address"]["housenumber"];
}
catch (const json::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
[json.exception.type_error.302] type must be number, but is string
```
This exception can be hard to debug if storing the value `"12"` and accessing it is further apart.
Example 2: extended diagnostic messages
```
#include <iostream>
# define JSON_DIAGNOSTICS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
json j;
j["address"]["street"] = "Fake Street";
j["address"]["housenumber"] = "12";
try
{
int housenumber = j["address"]["housenumber"];
}
catch (const json::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
[json.exception.type_error.302] (/address/housenumber) type must be number, but is string
```
Now the exception message contains a JSON Pointer `/address/housenumber` that indicates which value has the wrong type.
Example 3: using only diagnostic positions in exceptions
```
#include <iostream>
#define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
/* Demonstration of type error exception with diagnostic positions support enabled */
int main()
{
//Invalid json string - housenumber type must be int instead of string
const std::string json_invalid_string = R"(
{
"address": {
"street": "Fake Street",
"housenumber": "1"
}
}
)";
json j = json::parse(json_invalid_string);
try
{
int housenumber = j["address"]["housenumber"];
std::cout << housenumber;
}
catch (const json::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
[json.exception.type_error.302] (bytes 92-95) type must be number, but is string
```
The output shows the exception with start/end positions only.
## See also
- [JSON_Diagnostics](https://json.nlohmann.me/integration/cmake/#json_diagnostics) - CMake option to control the macro
- [JSON_DIAGNOSTIC_POSITIONS](https://json.nlohmann.me/api/macros/json_diagnostic_positions/index.md) - macro to access positions of elements
## Version history
- Added in version 3.10.0.
- As of version 3.11.0, the definition is allowed to vary between translation units.
@@ -0,0 +1,153 @@
# JSON_DISABLE_ENUM_SERIALIZATION
```cpp
#define JSON_DISABLE_ENUM_SERIALIZATION /* value */
```
When defined to `1`, default serialization and deserialization functions for enums are excluded and have to be provided
by the user, for example, using [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) (see
[arbitrary type conversions](../../features/arbitrary_types.md) for more details).
Parsing or serializing an enum will result in a compiler error.
This works for both unscoped and scoped enums.
## Default definition
The default value is `0`.
```cpp
#define JSON_DISABLE_ENUM_SERIALIZATION 0
```
## Notes
!!! hint "CMake option"
Enum serialization can also be controlled with the CMake option
[`JSON_DisableEnumSerialization`](../../integration/cmake.md#json_disableenumserialization)
(`OFF` by default) which defines `JSON_DISABLE_ENUM_SERIALIZATION` accordingly.
## Examples
??? example "Example 1: Disabled behavior"
The code below forces the library **not** to create default serialization/deserialization functions `from_json` and `to_json`, meaning the code below
**does not** compile.
```cpp
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
enum class Choice
{
first,
second,
};
int main()
{
// normally invokes to_json serialization function but with JSON_DISABLE_ENUM_SERIALIZATION defined, it does not
const json j = Choice::first;
// normally invokes from_json parse function but with JSON_DISABLE_ENUM_SERIALIZATION defined, it does not
Choice ch = j.get<Choice>();
}
```
??? example "Example 2: Serialize enum macro"
The code below forces the library **not** to create default serialization/deserialization functions `from_json` and `to_json`, but uses
[`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) to parse and serialize the enum.
```cpp
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
enum class Choice
{
first,
second,
};
NLOHMANN_JSON_SERIALIZE_ENUM(Choice,
{
{ Choice::first, "first" },
{ Choice::second, "second" },
})
int main()
{
// uses user-defined to_json function defined by macro
const json j = Choice::first;
// uses user-defined from_json function defined by macro
Choice ch = j.get<Choice>();
}
```
??? example "Example 3: User-defined serialization/deserialization functions"
The code below forces the library **not** to create default serialization/deserialization functions `from_json` and `to_json`, but uses user-defined
functions to parse and serialize the enum.
```cpp
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
enum class Choice
{
first,
second,
};
void from_json(const json& j, Choice& ch)
{
auto value = j.get<std::string>();
if (value == "first")
{
ch = Choice::first;
}
else if (value == "second")
{
ch = Choice::second;
}
}
void to_json(json& j, const Choice& ch)
{
if (ch == Choice::first)
{
j = "first";
}
else if (ch == Choice::second)
{
j = "second";
}
}
int main()
{
// uses user-defined to_json function
const json j = Choice::first;
// uses user-defined from_json function
Choice ch = j.get<Choice>();
}
```
## See also
- [:simple-cmake: JSON_DisableEnumSerialization](../../integration/cmake.md#json_disableenumserialization) - CMake option to control
the macro
- [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) - serialize/deserialize an enum
## Version history
- Added in version 3.11.0.
@@ -88,4 +88,4 @@
<span class=w> </span><span class=c1>// uses user-defined from_json function</span>
<span class=w> </span><span class=n>Choice</span><span class=w> </span><span class=n>ch</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>Choice</span><span class=o>&gt;</span><span class=p>();</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_disableenumserialization><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_DisableEnumSerialization</a> - CMake option to control the macro</li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> - serialize/deserialize an enum</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_disableenumserialization><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_DisableEnumSerialization</a> - CMake option to control the macro</li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> - serialize/deserialize an enum</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,145 @@
# JSON_DISABLE_ENUM_SERIALIZATION
```
#define JSON_DISABLE_ENUM_SERIALIZATION /* value */
```
When defined to `1`, default serialization and deserialization functions for enums are excluded and have to be provided by the user, for example, using [`NLOHMANN_JSON_SERIALIZE_ENUM`](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/index.md) (see [arbitrary type conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) for more details).
Parsing or serializing an enum will result in a compiler error.
This works for both unscoped and scoped enums.
## Default definition
The default value is `0`.
```
#define JSON_DISABLE_ENUM_SERIALIZATION 0
```
## Notes
CMake option
Enum serialization can also be controlled with the CMake option [`JSON_DisableEnumSerialization`](https://json.nlohmann.me/integration/cmake/#json_disableenumserialization) (`OFF` by default) which defines `JSON_DISABLE_ENUM_SERIALIZATION` accordingly.
## Examples
Example 1: Disabled behavior
The code below forces the library **not** to create default serialization/deserialization functions `from_json` and `to_json`, meaning the code below **does not** compile.
```
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
enum class Choice
{
first,
second,
};
int main()
{
// normally invokes to_json serialization function but with JSON_DISABLE_ENUM_SERIALIZATION defined, it does not
const json j = Choice::first;
// normally invokes from_json parse function but with JSON_DISABLE_ENUM_SERIALIZATION defined, it does not
Choice ch = j.get<Choice>();
}
```
Example 2: Serialize enum macro
The code below forces the library **not** to create default serialization/deserialization functions `from_json` and `to_json`, but uses [`NLOHMANN_JSON_SERIALIZE_ENUM`](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/index.md) to parse and serialize the enum.
```
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
enum class Choice
{
first,
second,
};
NLOHMANN_JSON_SERIALIZE_ENUM(Choice,
{
{ Choice::first, "first" },
{ Choice::second, "second" },
})
int main()
{
// uses user-defined to_json function defined by macro
const json j = Choice::first;
// uses user-defined from_json function defined by macro
Choice ch = j.get<Choice>();
}
```
Example 3: User-defined serialization/deserialization functions
The code below forces the library **not** to create default serialization/deserialization functions `from_json` and `to_json`, but uses user-defined functions to parse and serialize the enum.
```
#define JSON_DISABLE_ENUM_SERIALIZATION 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
enum class Choice
{
first,
second,
};
void from_json(const json& j, Choice& ch)
{
auto value = j.get<std::string>();
if (value == "first")
{
ch = Choice::first;
}
else if (value == "second")
{
ch = Choice::second;
}
}
void to_json(json& j, const Choice& ch)
{
if (ch == Choice::first)
{
j = "first";
}
else if (ch == Choice::second)
{
j = "second";
}
}
int main()
{
// uses user-defined to_json function
const json j = Choice::first;
// uses user-defined from_json function
Choice ch = j.get<Choice>();
}
```
## See also
- [JSON_DisableEnumSerialization](https://json.nlohmann.me/integration/cmake/#json_disableenumserialization) - CMake option to control the macro
- [`NLOHMANN_JSON_SERIALIZE_ENUM`](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/index.md) - serialize/deserialize an enum
## Version history
- Added in version 3.11.0.
+47
View File
@@ -0,0 +1,47 @@
# JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20, JSON_HAS_CPP_23, JSON_HAS_CPP_26
```cpp
#define JSON_HAS_CPP_11
#define JSON_HAS_CPP_14
#define JSON_HAS_CPP_17
#define JSON_HAS_CPP_20
#define JSON_HAS_CPP_23
#define JSON_HAS_CPP_26
```
The library targets C++11, but also supports some features introduced in later C++ versions (e.g., `std::string_view`
support for C++17). For these new features, the library implements some preprocessor checks to determine the C++
standard. By defining any of these symbols, the internal check is overridden and the provided C++ version is
unconditionally assumed. This can be helpful for compilers that only implement parts of the standard and would be
detected incorrectly.
## Default definition
The default value is detected based on preprocessor macros such as `#!cpp __cplusplus`, `#!cpp _HAS_CXX17`, or
`#!cpp _MSVC_LANG`.
## Notes
- When the C++ standard is detected automatically, `#!cpp JSON_HAS_CPP_11` is always defined. When you override the
detection by defining one of these macros manually, the automatic detection is skipped entirely, so you should define
all applicable macros (including `#!cpp JSON_HAS_CPP_11`) yourself.
- All macros are undefined outside the library.
## Examples
??? example
The code below forces the library to use the C++14 standard:
```cpp
#define JSON_HAS_CPP_14 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.10.5.
- Added `JSON_HAS_CPP_23` in version 3.12.0.
- Added `JSON_HAS_CPP_26` in version 3.12.x.
+1 -1
View File
@@ -8,4 +8,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.5.</li> <li>Added <code>JSON_HAS_CPP_23</code> in version 3.12.0.</li> <li>Added <code>JSON_HAS_CPP_26</code> in version 3.12.x.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.5.</li> <li>Added <code>JSON_HAS_CPP_23</code> in version 3.12.0.</li> <li>Added <code>JSON_HAS_CPP_26</code> in version 3.12.x.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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# JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20, JSON_HAS_CPP_23, JSON_HAS_CPP_26
```
#define JSON_HAS_CPP_11
#define JSON_HAS_CPP_14
#define JSON_HAS_CPP_17
#define JSON_HAS_CPP_20
#define JSON_HAS_CPP_23
#define JSON_HAS_CPP_26
```
The library targets C++11, but also supports some features introduced in later C++ versions (e.g., `std::string_view` support for C++17). For these new features, the library implements some preprocessor checks to determine the C++ standard. By defining any of these symbols, the internal check is overridden and the provided C++ version is unconditionally assumed. This can be helpful for compilers that only implement parts of the standard and would be detected incorrectly.
## Default definition
The default value is detected based on preprocessor macros such as `__cplusplus`, `_HAS_CXX17`, or `_MSVC_LANG`.
## Notes
- When the C++ standard is detected automatically, `JSON_HAS_CPP_11` is always defined. When you override the detection by defining one of these macros manually, the automatic detection is skipped entirely, so you should define all applicable macros (including `JSON_HAS_CPP_11`) yourself.
- All macros are undefined outside the library.
## Examples
Example
The code below forces the library to use the C++14 standard:
```
#define JSON_HAS_CPP_14 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.10.5.
- Added `JSON_HAS_CPP_23` in version 3.12.0.
- Added `JSON_HAS_CPP_26` in version 3.12.x.
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# JSON_HAS_FILESYSTEM / JSON_HAS_EXPERIMENTAL_FILESYSTEM
```cpp
#define JSON_HAS_FILESYSTEM /* value */
#define JSON_HAS_EXPERIMENTAL_FILESYSTEM /* value */
```
When compiling with C++17, the library provides conversions from and to
[`std::filesystem::path`](https://en.cppreference.com/w/cpp/filesystem/path). As compiler support for filesystem is
limited, the library tries to detect whether
[`<filesystem>`/`std::filesystem`](https://en.cppreference.com/w/cpp/header/filesystem) (`JSON_HAS_FILESYSTEM`) or
[`<experimental/filesystem>`/`std::experimental::filesystem`](https://en.cppreference.com/w/cpp/header/experimental/filesystem)
(`JSON_HAS_EXPERIMENTAL_FILESYSTEM`) should be used. To override the built-in check, define `JSON_HAS_FILESYSTEM` or
`JSON_HAS_EXPERIMENTAL_FILESYSTEM` to `1`.
## Default definition
The default value is detected based on the preprocessor macros `#!cpp __cpp_lib_filesystem`,
`#!cpp __cpp_lib_experimental_filesystem`, `#!cpp __has_include(<filesystem>)`, or
`#!cpp __has_include(<experimental/filesystem>)`.
## Notes
- Note that older compilers or older versions of libstdc++ also require the library `stdc++fs` to be linked to for
filesystem support.
- Both macros are undefined outside the library.
## Examples
??? example
The code below forces the library to use the header `<experimental/filesystem>`.
```cpp
#define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.10.5.
+1 -1
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@@ -4,4 +4,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.5.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.5.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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# JSON_HAS_FILESYSTEM / JSON_HAS_EXPERIMENTAL_FILESYSTEM
```
#define JSON_HAS_FILESYSTEM /* value */
#define JSON_HAS_EXPERIMENTAL_FILESYSTEM /* value */
```
When compiling with C++17, the library provides conversions from and to [`std::filesystem::path`](https://en.cppreference.com/w/cpp/filesystem/path). As compiler support for filesystem is limited, the library tries to detect whether [`<filesystem>`/`std::filesystem`](https://en.cppreference.com/w/cpp/header/filesystem) (`JSON_HAS_FILESYSTEM`) or [`<experimental/filesystem>`/`std::experimental::filesystem`](https://en.cppreference.com/w/cpp/header/experimental/filesystem) (`JSON_HAS_EXPERIMENTAL_FILESYSTEM`) should be used. To override the built-in check, define `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` to `1`.
## Default definition
The default value is detected based on the preprocessor macros `__cpp_lib_filesystem`, `__cpp_lib_experimental_filesystem`, `__has_include(<filesystem>)`, or `__has_include(<experimental/filesystem>)`.
## Notes
- Note that older compilers or older versions of libstdc++ also require the library `stdc++fs` to be linked to for filesystem support.
- Both macros are undefined outside the library.
## Examples
Example
The code below forces the library to use the header `<experimental/filesystem>`.
```
#define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.10.5.
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# JSON_HAS_RANGES
```cpp
#define JSON_HAS_RANGES /* value */
```
This macro indicates whether the standard library has any support for ranges. Implies support for concepts.
Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macro `#!cpp __cpp_lib_ranges`.
When the macro is not defined, the library will define it to its default value.
## Examples
??? example
The code below forces the library to enable support for ranges:
```cpp
#define JSON_HAS_RANGES 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.11.0.
+1 -1
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@@ -3,4 +3,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+30
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# JSON_HAS_RANGES
```
#define JSON_HAS_RANGES /* value */
```
This macro indicates whether the standard library has any support for ranges. Implies support for concepts. Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macro `__cpp_lib_ranges`.
When the macro is not defined, the library will define it to its default value.
## Examples
Example
The code below forces the library to enable support for ranges:
```
#define JSON_HAS_RANGES 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.11.0.
+31
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# JSON_HAS_STATIC_RTTI
```cpp
#define JSON_HAS_STATIC_RTTI /* value */
```
This macro indicates whether the standard library has any support for RTTI (run time type information).
Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macro `#!cpp _HAS_STATIC_RTTI`.
When the macro is not defined, the library will define it to its default value.
## Examples
??? example
The code below forces the library to enable support for libraries with RTTI dependence:
```cpp
#define JSON_HAS_STATIC_RTTI 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.11.3.
+1 -1
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@@ -3,4 +3,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.3.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.3.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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# JSON_HAS_STATIC_RTTI
```
#define JSON_HAS_STATIC_RTTI /* value */
```
This macro indicates whether the standard library has any support for RTTI (run time type information). Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macro `_HAS_STATIC_RTTI`.
When the macro is not defined, the library will define it to its default value.
## Examples
Example
The code below forces the library to enable support for libraries with RTTI dependence:
```
#define JSON_HAS_STATIC_RTTI 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.11.3.
+41
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# JSON_HAS_STD_FORMAT
```cpp
#define JSON_HAS_STD_FORMAT /* value */
```
This macro indicates whether the standard library has support for `std::format`/`std::formatter` (that
is, the `<format>` header). Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macros `#!cpp JSON_HAS_CPP_20` and
`#!cpp __cpp_lib_format`.
When the macro is not defined, the library will define it to its default value.
## Notes
!!! info "Enabled functionality"
When this macro evaluates to `1`, the library provides a
[`std::formatter<basic_json>`](../basic_json/std_formatter.md) specialization so JSON values can be
used directly with `std::format`.
## Examples
??? example
The code below forces the library to disable support for `std::format`, even if the standard library
would otherwise support it:
```cpp
#define JSON_HAS_STD_FORMAT 0
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.12.x.
+1 -1
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@@ -3,4 +3,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.x.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.x.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+36
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@@ -0,0 +1,36 @@
# JSON_HAS_STD_FORMAT
```
#define JSON_HAS_STD_FORMAT /* value */
```
This macro indicates whether the standard library has support for `std::format`/`std::formatter` (that is, the `<format>` header). Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macros `JSON_HAS_CPP_20` and `__cpp_lib_format`.
When the macro is not defined, the library will define it to its default value.
## Notes
Enabled functionality
When this macro evaluates to `1`, the library provides a [`std::formatter<basic_json>`](https://json.nlohmann.me/api/basic_json/std_formatter/index.md) specialization so JSON values can be used directly with `std::format`.
## Examples
Example
The code below forces the library to disable support for `std::format`, even if the standard library would otherwise support it:
```
#define JSON_HAS_STD_FORMAT 0
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.12.x.
@@ -0,0 +1,32 @@
# JSON_HAS_THREE_WAY_COMPARISON
```cpp
#define JSON_HAS_THREE_WAY_COMPARISON /* value */
```
This macro indicates whether the compiler and standard library support 3-way comparison.
Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macros `#!cpp __cpp_impl_three_way_comparison`
and `#!cpp __cpp_lib_three_way_comparison`.
When the macro is not defined, the library will define it to its default value.
## Examples
??? example
The code below forces the library to use 3-way comparison:
```cpp
#define JSON_HAS_THREE_WAY_COMPARISON 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.11.0.
@@ -3,4 +3,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,30 @@
# JSON_HAS_THREE_WAY_COMPARISON
```
#define JSON_HAS_THREE_WAY_COMPARISON /* value */
```
This macro indicates whether the compiler and standard library support 3-way comparison. Possible values are `1` when supported or `0` when unsupported.
## Default definition
The default value is detected based on the preprocessor macros `__cpp_impl_three_way_comparison` and `__cpp_lib_three_way_comparison`.
When the macro is not defined, the library will define it to its default value.
## Examples
Example
The code below forces the library to use 3-way comparison:
```
#define JSON_HAS_THREE_WAY_COMPARISON 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.11.0.
+35
View File
@@ -0,0 +1,35 @@
# JSON_NO_IO
```cpp
#define JSON_NO_IO
```
When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>` are not included and parse functions
relying on these headers are excluded. This is relevant for environments where these I/O functions are disallowed for
security reasons (e.g., Intel Software Guard Extensions (SGX)).
## Default definition
By default, `#!cpp JSON_NO_IO` is not defined.
```cpp
#undef JSON_NO_IO
```
## Examples
??? example
The code below forces the library not to use the headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and
`<ostream>`.
```cpp
#define JSON_NO_IO 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.10.0.
+1 -1
View File
@@ -4,4 +4,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.10.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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# JSON_NO_IO
```
#define JSON_NO_IO
```
When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>` are not included and parse functions relying on these headers are excluded. This is relevant for environments where these I/O functions are disallowed for security reasons (e.g., Intel Software Guard Extensions (SGX)).
## Default definition
By default, `JSON_NO_IO` is not defined.
```
#undef JSON_NO_IO
```
## Examples
Example
The code below forces the library not to use the headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>`.
```
#define JSON_NO_IO 1
#include <nlohmann/json.hpp>
...
```
## Version history
- Added in version 3.10.0.
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# JSON_NOEXCEPTION
```cpp
#define JSON_NOEXCEPTION
```
Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`. When defining `JSON_NOEXCEPTION`, `#!cpp try`
is replaced by `#!cpp if (true)`, `#!cpp catch` is replaced by `#!cpp if (false)`, and `#!cpp throw` is replaced by
`#!cpp std::abort()`.
The same effect is achieved by setting the compiler flag `-fno-exceptions`.
## Default definition
By default, the macro is not defined.
```cpp
#undef JSON_NOEXCEPTION
```
## Notes
The explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not
available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824).
## Examples
??? example
The code below switches off exceptions in the library.
```cpp
#define JSON_NOEXCEPTION 1
#include <nlohmann/json.hpp>
...
```
## See also
- [Switch off exceptions](../../home/exceptions.md#switch-off-exceptions) for more information how to switch off exceptions
## Version history
Added in version 2.1.0.
+1 -1
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@@ -4,4 +4,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/exceptions/#switch-off-exceptions>Switch off exceptions</a> for more information how to switch off exceptions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 2.1.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/exceptions/#switch-off-exceptions>Switch off exceptions</a> for more information how to switch off exceptions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 2.1.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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# JSON_NOEXCEPTION
```
#define JSON_NOEXCEPTION
```
Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`. When defining `JSON_NOEXCEPTION`, `try` is replaced by `if (true)`, `catch` is replaced by `if (false)`, and `throw` is replaced by `std::abort()`.
The same effect is achieved by setting the compiler flag `-fno-exceptions`.
## Default definition
By default, the macro is not defined.
```
#undef JSON_NOEXCEPTION
```
## Notes
The explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824).
## Examples
Example
The code below switches off exceptions in the library.
```
#define JSON_NOEXCEPTION 1
#include <nlohmann/json.hpp>
...
```
## See also
- [Switch off exceptions](https://json.nlohmann.me/home/exceptions/#switch-off-exceptions) for more information how to switch off exceptions
## Version history
Added in version 2.1.0.
@@ -0,0 +1,48 @@
# JSON_SKIP_LIBRARY_VERSION_CHECK
```cpp
#define JSON_SKIP_LIBRARY_VERSION_CHECK
```
When defined, the library will not create a compiler warning when a different version of the library was already
included.
## Default definition
By default, the macro is not defined.
```cpp
#undef JSON_SKIP_LIBRARY_VERSION_CHECK
```
## Notes
!!! danger "ABI compatibility"
Mixing different library versions in the same code can be a problem as the different versions may not be ABI
compatible.
## Examples
??? example
The code below switches off the warning about including a different version of the library.
```cpp
#define JSON_SKIP_LIBRARY_VERSION_CHECK 1
#include <nlohmann/json.hpp>
...
```
!!! example
The following warning will be shown in case a different version of the library was already included:
```
Already included a different version of the library!
```
## Version history
Added in version 3.11.0.
@@ -5,4 +5,4 @@
<span class=p>...</span>
</code></pre></div> </details> <div class="admonition example"> <p class=admonition-title>Example</p> <p>The following warning will be shown in case a different version of the library was already included:</p> <div class=highlight><pre><span></span><code>Already included a different version of the library!
</code></pre></div> </div> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.11.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </div> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.11.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,46 @@
# JSON_SKIP_LIBRARY_VERSION_CHECK
```
#define JSON_SKIP_LIBRARY_VERSION_CHECK
```
When defined, the library will not create a compiler warning when a different version of the library was already included.
## Default definition
By default, the macro is not defined.
```
#undef JSON_SKIP_LIBRARY_VERSION_CHECK
```
## Notes
ABI compatibility
Mixing different library versions in the same code can be a problem as the different versions may not be ABI compatible.
## Examples
Example
The code below switches off the warning about including a different version of the library.
```
#define JSON_SKIP_LIBRARY_VERSION_CHECK 1
#include <nlohmann/json.hpp>
...
```
Example
The following warning will be shown in case a different version of the library was already included:
```
Already included a different version of the library!
```
## Version history
Added in version 3.11.0.
@@ -0,0 +1,33 @@
# JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
```cpp
#define JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
```
When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows
using the library with compilers that do not fully support C++11 and may only work if unsupported features are not used.
## Default definition
By default, the macro is not defined.
```cpp
#undef JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
```
## Examples
??? example
The code below switches off the check whether the compiler is supported.
```cpp
#define JSON_SKIP_UNSUPPORTED_COMPILER_CHECK 1
#include <nlohmann/json.hpp>
...
```
## Version history
Added in version 3.2.0.
@@ -4,4 +4,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.2.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.2.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,32 @@
# JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
```
#define JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
```
When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows using the library with compilers that do not fully support C++11 and may only work if unsupported features are not used.
## Default definition
By default, the macro is not defined.
```
#undef JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
```
## Examples
Example
The code below switches off the check whether the compiler is supported.
```
#define JSON_SKIP_UNSUPPORTED_COMPILER_CHECK 1
#include <nlohmann/json.hpp>
...
```
## Version history
Added in version 3.2.0.
+75
View File
@@ -0,0 +1,75 @@
# JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER
```cpp
// (1)
#define JSON_CATCH_USER(exception) /* value */
// (2)
#define JSON_THROW_USER(exception) /* value */
// (3)
#define JSON_TRY_USER /* value */
```
Controls how exceptions are handled by the library.
1. This macro overrides [`#!cpp catch`](https://en.cppreference.com/w/cpp/language/try_catch) calls inside the library.
The argument is the type of the exception to catch. As of version 3.8.0, the library only catches `std::out_of_range`
exceptions internally to rethrow them as [`json::out_of_range`](../../home/exceptions.md#out-of-range) exceptions.
The macro is always followed by a scope.
2. This macro overrides `#!cpp throw` calls inside the library. The argument is the exception to be thrown. Note that
`JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield
undefined behavior.
3. This macro overrides `#!cpp try` calls inside the library. It has no arguments and is always followed by a scope.
## Parameters
`exception` (in)
: an exception type
## Default definition
By default, the macros map to their respective C++ keywords:
```cpp
#define JSON_CATCH_USER(exception) catch(exception)
#define JSON_THROW_USER(exception) throw exception
#define JSON_TRY_USER try
```
When exceptions are switched off, the `#!cpp try` block is executed unconditionally, and throwing exceptions is
replaced by calling [`std::abort`](https://en.cppreference.com/w/cpp/utility/program/abort) to make reaching the
`#!cpp throw` branch abort the process.
```cpp
#define JSON_THROW_USER(exception) std::abort()
#define JSON_TRY_USER if (true)
#define JSON_CATCH_USER(exception) if (false)
```
## Examples
??? example
The code below switches off exceptions and creates a log entry with a detailed error message in case of errors.
```cpp
#include <iostream>
#define JSON_TRY_USER if(true)
#define JSON_CATCH_USER(exception) if(false)
#define JSON_THROW_USER(exception) \
{std::clog << "Error in " << __FILE__ << ":" << __LINE__ \
<< " (function " << __FUNCTION__ << ") - " \
<< (exception).what() << std::endl; \
std::abort();}
#include <nlohmann/json.hpp>
```
## See also
- [Switch off exceptions](../../home/exceptions.md#switch-off-exceptions) for more information how to switch off exceptions
- [JSON_NOEXCEPTION](json_noexception.md) - switch off exceptions
## Version history
- Added in version 3.1.0.
+1 -1
View File
@@ -21,4 +21,4 @@
<span class=cp> std::abort();}</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/exceptions/#switch-off-exceptions>Switch off exceptions</a> for more information how to switch off exceptions</li> <li><a href=../json_noexception/ >JSON_NOEXCEPTION</a> - switch off exceptions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../home/exceptions/#switch-off-exceptions>Switch off exceptions</a> for more information how to switch off exceptions</li> <li><a href=../json_noexception/ >JSON_NOEXCEPTION</a> - switch off exceptions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+67
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@@ -0,0 +1,67 @@
# JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER
```
// (1)
#define JSON_CATCH_USER(exception) /* value */
// (2)
#define JSON_THROW_USER(exception) /* value */
// (3)
#define JSON_TRY_USER /* value */
```
Controls how exceptions are handled by the library.
1. This macro overrides [`catch`](https://en.cppreference.com/w/cpp/language/try_catch) calls inside the library. The argument is the type of the exception to catch. As of version 3.8.0, the library only catches `std::out_of_range` exceptions internally to rethrow them as [`json::out_of_range`](https://json.nlohmann.me/home/exceptions/#out-of-range) exceptions. The macro is always followed by a scope.
1. This macro overrides `throw` calls inside the library. The argument is the exception to be thrown. Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior.
1. This macro overrides `try` calls inside the library. It has no arguments and is always followed by a scope.
## Parameters
`exception` (in) : an exception type
## Default definition
By default, the macros map to their respective C++ keywords:
```
#define JSON_CATCH_USER(exception) catch(exception)
#define JSON_THROW_USER(exception) throw exception
#define JSON_TRY_USER try
```
When exceptions are switched off, the `try` block is executed unconditionally, and throwing exceptions is replaced by calling [`std::abort`](https://en.cppreference.com/w/cpp/utility/program/abort) to make reaching the `throw` branch abort the process.
```
#define JSON_THROW_USER(exception) std::abort()
#define JSON_TRY_USER if (true)
#define JSON_CATCH_USER(exception) if (false)
```
## Examples
Example
The code below switches off exceptions and creates a log entry with a detailed error message in case of errors.
```
#include <iostream>
#define JSON_TRY_USER if(true)
#define JSON_CATCH_USER(exception) if(false)
#define JSON_THROW_USER(exception) \
{std::clog << "Error in " << __FILE__ << ":" << __LINE__ \
<< " (function " << __FUNCTION__ << ") - " \
<< (exception).what() << std::endl; \
std::abort();}
#include <nlohmann/json.hpp>
```
## See also
- [Switch off exceptions](https://json.nlohmann.me/home/exceptions/#switch-off-exceptions) for more information how to switch off exceptions
- [JSON_NOEXCEPTION](https://json.nlohmann.me/api/macros/json_noexception/index.md) - switch off exceptions
## Version history
- Added in version 3.1.0.
+99
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# JSON_USE_GLOBAL_UDLS
```cpp
#define JSON_USE_GLOBAL_UDLS /* value */
```
When defined to `1`, the user-defined string literals (UDLs) are placed into the global namespace instead of
`nlohmann::literals::json_literals`.
## Default definition
The default value is `1`.
```cpp
#define JSON_USE_GLOBAL_UDLS 1
```
When the macro is not defined, the library will define it to its default value.
## Notes
!!! info "Future behavior change"
The user-defined string literals will be removed from the global namespace in the next major release of the library.
To prepare existing code, define `JSON_USE_GLOBAL_UDLS` to `0` and bring the string literals into scope where
needed. Refer to any of the [string literals](#see-also) for details.
!!! hint "CMake option"
The placement of user-defined string literals can also be controlled with the CMake option
[`JSON_GlobalUDLs`](../../integration/cmake.md#json_globaludls) (`ON` by default) which defines
`JSON_USE_GLOBAL_UDLS` accordingly.
## Examples
??? example "Example 1: Default behavior"
The code below shows the default behavior using the `_json` UDL.
```cpp
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
auto j = "42"_json;
std::cout << j << std::endl;
}
```
Output:
```json
42
```
??? example "Example 2: Namespaced UDLs"
The code below shows how UDLs need to be brought into scope before using `_json` when `JSON_USE_GLOBAL_UDLS` is
defined to `0`.
```cpp
#define JSON_USE_GLOBAL_UDLS 0
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
// auto j = "42"_json; // This line would fail to compile,
// because the UDLs are not in the global namespace
// Bring the UDLs into scope
using namespace nlohmann::json_literals;
auto j = "42"_json;
std::cout << j << std::endl;
}
```
Output:
```json
42
```
## See also
- [`operator""_json`](../operator_literal_json.md)
- [`operator""_json_pointer`](../operator_literal_json_pointer.md)
- [:simple-cmake: JSON_GlobalUDLs](../../integration/cmake.md#json_globaludls) - CMake option to control the macro
## Version history
- Added in version 3.11.0.
+1 -1
View File
@@ -29,4 +29,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>42</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../operator_literal_json/ ><code>operator""_json</code></a></li> <li><a href=../../operator_literal_json_pointer/ ><code>operator""_json_pointer</code></a></li> <li><a href=../../../integration/cmake/#json_globaludls><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_GlobalUDLs</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../operator_literal_json/ ><code>operator""_json</code></a></li> <li><a href=../../operator_literal_json_pointer/ ><code>operator""_json_pointer</code></a></li> <li><a href=../../../integration/cmake/#json_globaludls><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_GlobalUDLs</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+94
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@@ -0,0 +1,94 @@
# JSON_USE_GLOBAL_UDLS
```
#define JSON_USE_GLOBAL_UDLS /* value */
```
When defined to `1`, the user-defined string literals (UDLs) are placed into the global namespace instead of `nlohmann::literals::json_literals`.
## Default definition
The default value is `1`.
```
#define JSON_USE_GLOBAL_UDLS 1
```
When the macro is not defined, the library will define it to its default value.
## Notes
Future behavior change
The user-defined string literals will be removed from the global namespace in the next major release of the library.
To prepare existing code, define `JSON_USE_GLOBAL_UDLS` to `0` and bring the string literals into scope where needed. Refer to any of the [string literals](#see-also) for details.
CMake option
The placement of user-defined string literals can also be controlled with the CMake option [`JSON_GlobalUDLs`](https://json.nlohmann.me/integration/cmake/#json_globaludls) (`ON` by default) which defines `JSON_USE_GLOBAL_UDLS` accordingly.
## Examples
Example 1: Default behavior
The code below shows the default behavior using the `_json` UDL.
```
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
auto j = "42"_json;
std::cout << j << std::endl;
}
```
Output:
```
42
```
Example 2: Namespaced UDLs
The code below shows how UDLs need to be brought into scope before using `_json` when `JSON_USE_GLOBAL_UDLS` is defined to `0`.
```
#define JSON_USE_GLOBAL_UDLS 0
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
// auto j = "42"_json; // This line would fail to compile,
// because the UDLs are not in the global namespace
// Bring the UDLs into scope
using namespace nlohmann::json_literals;
auto j = "42"_json;
std::cout << j << std::endl;
}
```
Output:
```
42
```
## See also
- [`operator""_json`](https://json.nlohmann.me/api/operator_literal_json/index.md)
- [`operator""_json_pointer`](https://json.nlohmann.me/api/operator_literal_json_pointer/index.md)
- [JSON_GlobalUDLs](https://json.nlohmann.me/integration/cmake/#json_globaludls) - CMake option to control the macro
## Version history
- Added in version 3.11.0.
@@ -0,0 +1,60 @@
# JSON_USE_IMPLICIT_CONVERSIONS
```cpp
#define JSON_USE_IMPLICIT_CONVERSIONS /* value */
```
When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on. The
value directly affects [`operator ValueType`](../basic_json/operator_ValueType.md).
## Default definition
By default, implicit conversions are enabled.
```cpp
#define JSON_USE_IMPLICIT_CONVERSIONS 1
```
## Notes
!!! info "Future behavior change"
Implicit conversions will be switched off by default in the next major release of the library.
You can prepare existing code by already defining `JSON_USE_IMPLICIT_CONVERSIONS` to `0` and replace any implicit
conversions with calls to [`get`](../basic_json/get.md).
!!! hint "CMake option"
Implicit conversions can also be controlled with the CMake option
[`JSON_ImplicitConversions`](../../integration/cmake.md#json_implicitconversions)
(`ON` by default) which defines `JSON_USE_IMPLICIT_CONVERSIONS` accordingly.
## Examples
??? example
This is an example for an implicit conversion:
```cpp
json j = "Hello, world!";
std::string s = j;
```
When `JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`, the code above does no longer compile. Instead, it must be
written like this:
```cpp
json j = "Hello, world!";
auto s = j.get<std::string>();
```
## See also
- [**operator ValueType**](../basic_json/operator_ValueType.md) - get a value (implicit)
- [**get**](../basic_json/get.md) - get a value (explicit)
- [:simple-cmake: JSON_ImplicitConversions](../../integration/cmake.md#json_implicitconversions) - CMake option to control the macro
## Version history
- Added in version 3.9.0.
@@ -4,4 +4,4 @@
<span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>s</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
</code></pre></div> <p>When <code>JSON_USE_IMPLICIT_CONVERSIONS</code> is defined to <code>0</code>, the code above does no longer compile. Instead, it must be written like this:</p> <div class=highlight><pre><span></span><code><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>&quot;Hello, world!&quot;</span><span class=p>;</span>
<span class=k>auto</span><span class=w> </span><span class=n>s</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=o>&gt;</span><span class=p>();</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/operator_ValueType/ ><strong>operator ValueType</strong></a> - get a value (implicit)</li> <li><a href=../../basic_json/get/ ><strong>get</strong></a> - get a value (explicit)</li> <li><a href=../../../integration/cmake/#json_implicitconversions><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_ImplicitConversions</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/operator_ValueType/ ><strong>operator ValueType</strong></a> - get a value (implicit)</li> <li><a href=../../basic_json/get/ ><strong>get</strong></a> - get a value (explicit)</li> <li><a href=../../../integration/cmake/#json_implicitconversions><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_ImplicitConversions</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V31Line truncated
@@ -0,0 +1,55 @@
# JSON_USE_IMPLICIT_CONVERSIONS
```
#define JSON_USE_IMPLICIT_CONVERSIONS /* value */
```
When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on. The value directly affects [`operator ValueType`](https://json.nlohmann.me/api/basic_json/operator_ValueType/index.md).
## Default definition
By default, implicit conversions are enabled.
```
#define JSON_USE_IMPLICIT_CONVERSIONS 1
```
## Notes
Future behavior change
Implicit conversions will be switched off by default in the next major release of the library.
You can prepare existing code by already defining `JSON_USE_IMPLICIT_CONVERSIONS` to `0` and replace any implicit conversions with calls to [`get`](https://json.nlohmann.me/api/basic_json/get/index.md).
CMake option
Implicit conversions can also be controlled with the CMake option [`JSON_ImplicitConversions`](https://json.nlohmann.me/integration/cmake/#json_implicitconversions) (`ON` by default) which defines `JSON_USE_IMPLICIT_CONVERSIONS` accordingly.
## Examples
Example
This is an example for an implicit conversion:
```
json j = "Hello, world!";
std::string s = j;
```
When `JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`, the code above does no longer compile. Instead, it must be written like this:
```
json j = "Hello, world!";
auto s = j.get<std::string>();
```
## See also
- [**operator ValueType**](https://json.nlohmann.me/api/basic_json/operator_ValueType/index.md) - get a value (implicit)
- [**get**](https://json.nlohmann.me/api/basic_json/get/index.md) - get a value (explicit)
- [JSON_ImplicitConversions](https://json.nlohmann.me/integration/cmake/#json_implicitconversions) - CMake option to control the macro
## Version history
- Added in version 3.9.0.
@@ -0,0 +1,81 @@
# JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
```cpp
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON /* value */
```
This macro enables the (incorrect) legacy comparison behavior of discarded JSON values. Possible values are `1` to
enable or `0` to disable (default).
When enabled, comparisons involving at least one discarded JSON value yield results as follows:
| **Operator** | **Result** |
|--------------|---------------|
| `==` | `#!cpp false` |
| `!=` | `#!cpp true` |
| `<` | `#!cpp false` |
| `<=` | `#!cpp true` |
| `>=` | `#!cpp true` |
| `>` | `#!cpp false` |
Otherwise, comparisons involving at least one discarded JSON value always yield `#!cpp false`.
## Default definition
The default value is `0`.
```cpp
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0
```
When the macro is not defined, the library will define it to its default value.
## Notes
!!! warning "Inconsistent behavior in C++20 and beyond"
When targeting C++20 or above, enabling the legacy comparison behavior is _strongly_
discouraged.
- The 3-way comparison operator (`<=>`) will always give the correct result
(`#!cpp std::partial_ordering::unordered`) regardless of the value of
`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`.
- Overloads for the equality and relational operators emulate the legacy behavior.
Code outside your control may use either 3-way comparison or the equality and relational operators, resulting in
inconsistent and unpredictable behavior.
See [`operator<=>`](../basic_json/operator_spaceship.md) for more information on 3-way comparison.
!!! warning "Deprecation"
The legacy comparison behavior is deprecated and may be removed in a future major version release.
New code should not depend on it and existing code should try to remove or rewrite expressions relying on it.
!!! hint "CMake option"
Legacy comparison can also be controlled with the CMake option
[`JSON_LegacyDiscardedValueComparison`](../../integration/cmake.md#json_legacydiscardedvaluecomparison)
(`OFF` by default) which defines `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON` accordingly.
## Examples
??? example
The code below switches on the legacy discarded value comparison behavior in the library.
```cpp
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 1
#include <nlohmann/json.hpp>
...
```
## See also
- [:simple-cmake: JSON_LegacyDiscardedValueComparison](../../integration/cmake.md#json_legacydiscardedvaluecomparison) - CMake option to control the macro
## Version history
- Added in version 3.11.0.
@@ -4,4 +4,4 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=p>...</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_legacydiscardedvaluecomparison><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_LegacyDiscardedValueComparison</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../integration/cmake/#json_legacydiscardedvaluecomparison><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_LegacyDiscardedValueComparison</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,74 @@
# JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
```
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON /* value */
```
This macro enables the (incorrect) legacy comparison behavior of discarded JSON values. Possible values are `1` to enable or `0` to disable (default).
When enabled, comparisons involving at least one discarded JSON value yield results as follows:
| **Operator** | **Result** |
| ------------ | ---------- |
| `==` | `false` |
| `!=` | `true` |
| `<` | `false` |
| `<=` | `true` |
| `>=` | `true` |
| `>` | `false` |
Otherwise, comparisons involving at least one discarded JSON value always yield `false`.
## Default definition
The default value is `0`.
```
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0
```
When the macro is not defined, the library will define it to its default value.
## Notes
Inconsistent behavior in C++20 and beyond
When targeting C++20 or above, enabling the legacy comparison behavior is *strongly* discouraged.
- The 3-way comparison operator (`<=>`) will always give the correct result (`std::partial_ordering::unordered`) regardless of the value of `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`.
- Overloads for the equality and relational operators emulate the legacy behavior.
Code outside your control may use either 3-way comparison or the equality and relational operators, resulting in inconsistent and unpredictable behavior.
See [`operator<=>`](https://json.nlohmann.me/api/basic_json/operator_spaceship/index.md) for more information on 3-way comparison.
Deprecation
The legacy comparison behavior is deprecated and may be removed in a future major version release.
New code should not depend on it and existing code should try to remove or rewrite expressions relying on it.
CMake option
Legacy comparison can also be controlled with the CMake option [`JSON_LegacyDiscardedValueComparison`](https://json.nlohmann.me/integration/cmake/#json_legacydiscardedvaluecomparison) (`OFF` by default) which defines `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON` accordingly.
## Examples
Example
The code below switches on the legacy discarded value comparison behavior in the library.
```
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 1
#include <nlohmann/json.hpp>
...
```
## See also
- [JSON_LegacyDiscardedValueComparison](https://json.nlohmann.me/integration/cmake/#json_legacydiscardedvaluecomparison) - CMake option to control the macro
## Version history
- Added in version 3.11.0.
+177
View File
@@ -0,0 +1,177 @@
<h1>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE,
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</h1>
```cpp
// (1)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(type, base_type, member...)
// (2)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)
// (3)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)
// (4)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(type, base_type, member...)
// (5)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)
// (6)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)
```
These macros can be used to simplify the serialization/deserialization of derived types if you want to use a JSON
object as serialization and want to use the member variable names as object keys in that object.
- Macros 1, 2, and 3 are to be defined **inside** the class/struct to create code for.
Like [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](nlohmann_define_type_intrusive.md), they can access private members.
- Macros 4, 5, and 6 are to be defined **outside** the class/struct to create code for, but **inside** its namespace.
Like [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](nlohmann_define_type_non_intrusive.md),
they **cannot** access private members.
The first parameter is the name of the derived class/struct,
the second parameter is the name of the base class/struct and all remaining parameters name the members.
The base type **must** be already serializable/deserializable.
- Macros 1 and 4 will use [`at`](../basic_json/at.md) during deserialization and will throw
[`out_of_range.403`](../../home/exceptions.md#jsonexceptionout_of_range403) if a key is missing in the JSON object.
- Macros 2 and 5 will use [`value`](../basic_json/value.md) during deserialization and fall back to the default value for the
respective type of the member variable if a key in the JSON object is missing. The generated `from_json()` function
default constructs an object and uses its values as the defaults when calling the `value` function.
Summary:
| Need access to private members | Need only serialization | Allow missing values when de-serializing | macro |
|------------------------------------------------------------------|------------------------------------------------------------------|------------------------------------------------------------------|---------------------------------------------------------------|
| <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | **NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE** |
| <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | **NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT** |
| <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: grey;">:octicons-skip-fill-24:</div> | **NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE** |
| <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | **NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE** |
| <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | **NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT** |
| <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: grey;">:octicons-skip-fill-24:</div> | **NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE** |
## Parameters
`type` (in)
: name of the type (class, struct) to serialize/deserialize
`base_type` (in)
: name of the base type (class, struct) `type` is derived from
`member` (in)
: name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
## Default definition
Macros 1 and 2 add two friend functions to the class which take care of the serialization and deserialization:
```cpp
template<typename BasicJsonType>
friend void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
friend void from_json(const BasicJsonType&, type&);
```
Macros 4 and 5 add two functions to the namespace which take care of the serialization and deserialization:
```cpp
template<typename BasicJsonType>
void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
void from_json(const BasicJsonType&, type&);
```
Macros 3 and 6 add one function to the namespace, which takes care of the serialization only:
```cpp
template<typename BasicJsonType>
void to_json(BasicJsonType&, const type&);
```
In first two cases, they call the `to_json`/`from_json` functions of the base type
before serializing/deserializing the members of the derived type:
```cpp
class A { /* ... */ };
class B : public A { /* ... */ };
template<typename BasicJsonType>
void to_json(BasicJsonType& j, const B& b) {
nlohmann::to_json(j, static_cast<const A&>(b));
// ...
}
template<typename BasicJsonType>
void from_json(const BasicJsonType& j, B& b) {
nlohmann::from_json(j, static_cast<A&>(b));
// ...
}
```
In the third case, only `to_json` will be called:
```cpp
class A { /* ... */ };
class B : public A { /* ... */ };
template<typename BasicJsonType>
void to_json(BasicJsonType& j, const B& b) {
nlohmann::to_json(j, static_cast<const A&>(b));
// ...
}
```
## Notes
!!! info "Prerequisites"
- Macros 1, 2, and 3 have the same prerequisites of [NLOHMANN_DEFINE_TYPE_INTRUSIVE](nlohmann_define_type_intrusive.md).
- Macros 4, 5, and 6 have the same prerequisites of [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](nlohmann_define_type_non_intrusive.md).
- Serialization/deserialization of base types must be defined.
!!! warning "Implementation limits"
See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](nlohmann_define_type_intrusive.md) and
[NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](nlohmann_define_type_non_intrusive.md), respectively.
## Examples
??? example "NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE"
Consider the following complete example:
```cpp hl_lines="28"
--8<-- "examples/nlohmann_define_derived_type_intrusive_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_derived_type_intrusive_macro.output"
```
Notes:
- `A` and `B` are default-constructible. This is a requirement for using the macro.
- `A` has private members and is not a derived class. Hence, macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is used.
- As `B` is a derived class, `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is not applicable, but
`NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE` must be used.
- The macro `NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE` is used _inside_ the class use as
`NLOHMANN_DEFINE_TYPE_INTRUSIVE`.
## See also
- [NLOHMANN_DEFINE_TYPE_INTRUSIVE / NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT /
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE](nlohmann_define_type_intrusive.md)
for similar macros that can be defined _inside_ a non-derived type.
- [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT /
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](nlohmann_define_type_non_intrusive.md)
for similar macros that can be defined _outside_ a non-derived type.
- [Arbitrary Type Conversions](../../features/arbitrary_types.md) for an overview.
## Version history
1. Added in version 3.12.0.
2. Added in version 3.12.0.
3. Added in version 3.12.0.
4. Added in version 3.12.0.
5. Added in version 3.12.0.
6. Added in version 3.12.0.
@@ -86,4 +86,4 @@
<span class=w> </span><span class=nt>&quot;Ba&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>23</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;Bb&quot;</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=p>}</span>
</code></pre></div> <p>Notes:</p> <ul> <li><code>A</code> and <code>B</code> are default-constructible. This is a requirement for using the macro.</li> <li><code>A</code> has private members and is not a derived class. Hence, macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is used.</li> <li>As <code>B</code> is a derived class, <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is not applicable, but <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> must be used.</li> <li>The macro <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> is used <em>inside</em> the class use as <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code>.</li> </ul> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE / NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>inside</em> a non-derived type.</li> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>outside</em> a non-derived type.</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 Line truncated
</code></pre></div> <p>Notes:</p> <ul> <li><code>A</code> and <code>B</code> are default-constructible. This is a requirement for using the macro.</li> <li><code>A</code> has private members and is not a derived class. Hence, macro <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is used.</li> <li>As <code>B</code> is a derived class, <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code> is not applicable, but <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> must be used.</li> <li>The macro <code>NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE</code> is used <em>inside</em> the class use as <code>NLOHMANN_DEFINE_TYPE_INTRUSIVE</code>.</li> </ul> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE / NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>inside</em> a non-derived type.</li> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros that can be defined <em>outside</em> a non-derived type.</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> <li>Added in version 3.12.0.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 Line truncated
@@ -0,0 +1,196 @@
# NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE
```
// (1)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(type, base_type, member...)
// (2)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)
// (3)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)
// (4)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(type, base_type, member...)
// (5)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, base_type, member...)
// (6)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, base_type, member...)
```
These macros can be used to simplify the serialization/deserialization of derived types if you want to use a JSON object as serialization and want to use the member variable names as object keys in that object.
- Macros 1, 2, and 3 are to be defined **inside** the class/struct to create code for. Like [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md), they can access private members.
- Macros 4, 5, and 6 are to be defined **outside** the class/struct to create code for, but **inside** its namespace. Like [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md), they **cannot** access private members.
The first parameter is the name of the derived class/struct, the second parameter is the name of the base class/struct and all remaining parameters name the members. The base type **must** be already serializable/deserializable.
- Macros 1 and 4 will use [`at`](https://json.nlohmann.me/api/basic_json/at/index.md) during deserialization and will throw [`out_of_range.403`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range403) if a key is missing in the JSON object.
- Macros 2 and 5 will use [`value`](https://json.nlohmann.me/api/basic_json/value/index.md) during deserialization and fall back to the default value for the respective type of the member variable if a key in the JSON object is missing. The generated `from_json()` function default constructs an object and uses its values as the defaults when calling the `value` function.
Summary:
| Need access to private members | Need only serialization | Allow missing values when de-serializing | macro |
| ------------------------------ | ----------------------- | ---------------------------------------- | ------------------------------------------------------------- |
| | | | **NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE** |
| | | | **NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT** |
| | | | **NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE** |
| | | | **NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE** |
| | | | **NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT** |
| | | | **NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE** |
## Parameters
`type` (in) : name of the type (class, struct) to serialize/deserialize
`base_type` (in) : name of the base type (class, struct) `type` is derived from
`member` (in) : name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
## Default definition
Macros 1 and 2 add two friend functions to the class which take care of the serialization and deserialization:
```
template<typename BasicJsonType>
friend void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
friend void from_json(const BasicJsonType&, type&);
```
Macros 4 and 5 add two functions to the namespace which take care of the serialization and deserialization:
```
template<typename BasicJsonType>
void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
void from_json(const BasicJsonType&, type&);
```
Macros 3 and 6 add one function to the namespace, which takes care of the serialization only:
```
template<typename BasicJsonType>
void to_json(BasicJsonType&, const type&);
```
In first two cases, they call the `to_json`/`from_json` functions of the base type before serializing/deserializing the members of the derived type:
```
class A { /* ... */ };
class B : public A { /* ... */ };
template<typename BasicJsonType>
void to_json(BasicJsonType& j, const B& b) {
nlohmann::to_json(j, static_cast<const A&>(b));
// ...
}
template<typename BasicJsonType>
void from_json(const BasicJsonType& j, B& b) {
nlohmann::from_json(j, static_cast<A&>(b));
// ...
}
```
In the third case, only `to_json` will be called:
```
class A { /* ... */ };
class B : public A { /* ... */ };
template<typename BasicJsonType>
void to_json(BasicJsonType& j, const B& b) {
nlohmann::to_json(j, static_cast<const A&>(b));
// ...
}
```
## Notes
Prerequisites
- Macros 1, 2, and 3 have the same prerequisites of [NLOHMANN_DEFINE_TYPE_INTRUSIVE](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md).
- Macros 4, 5, and 6 have the same prerequisites of [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md).
- Serialization/deserialization of base types must be defined.
Implementation limits
See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) and [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md), respectively.
## Examples
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE
Consider the following complete example:
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using nlohmann::json;
class A
{
private:
double Aa = 0.0;
double Ab = 0.0;
public:
A() = default;
A(double a, double b) : Aa(a), Ab(b) {}
NLOHMANN_DEFINE_TYPE_INTRUSIVE(A, Aa, Ab)
};
class B : public A
{
private:
int Ba = 0;
int Bb = 0;
public:
B() = default;
B(int a, int b, double aa, double ab) : A(aa, ab), Ba(a), Bb(b) {}
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(B, A, Ba, Bb)
};
int main()
{
B example(23, 42, 3.142, 1.777);
json example_json = example;
std::cout << std::setw(4) << example_json << std::endl;
}
```
Output:
```
{
"Aa": 3.142,
"Ab": 1.777,
"Ba": 23,
"Bb": 42
}
```
Notes:
- `A` and `B` are default-constructible. This is a requirement for using the macro.
- `A` has private members and is not a derived class. Hence, macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is used.
- As `B` is a derived class, `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is not applicable, but `NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE` must be used.
- The macro `NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE` is used *inside* the class use as `NLOHMANN_DEFINE_TYPE_INTRUSIVE`.
## See also
- [NLOHMANN_DEFINE_TYPE_INTRUSIVE / NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) for similar macros that can be defined *inside* a non-derived type.
- [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT / NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md) for similar macros that can be defined *outside* a non-derived type.
- [Arbitrary Type Conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) for an overview.
## Version history
1. Added in version 3.12.0.
1. Added in version 3.12.0.
1. Added in version 3.12.0.
1. Added in version 3.12.0.
1. Added in version 3.12.0.
1. Added in version 3.12.0.
@@ -0,0 +1,170 @@
# NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE
```cpp
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...) // (1)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...) // (2)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, member...) // (3)
```
These macros can be used to simplify the serialization/deserialization of types if you want to use a JSON object as
serialization and want to use the member variable names as object keys in that object. The macro is to be defined
**inside** the class/struct to create code for. Unlike
[`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](nlohmann_define_type_non_intrusive.md), it can access private members. The first
parameter is the name of the class/struct, and all remaining parameters name the members.
1. Will use [`at`](../basic_json/at.md) during deserialization and will throw
[`out_of_range.403`](../../home/exceptions.md#jsonexceptionout_of_range403) if a key is missing in the JSON object.
2. Will use [`value`](../basic_json/value.md) during deserialization and fall back to the default value for the
respective type of the member variable if a key in the JSON object is missing. The generated `from_json()` function
default constructs an object and uses its values as the defaults when calling the `value` function.
3. Only defines the serialization. Useful in cases when the type does not have a default constructor and only serialization is required.
Summary:
| Need access to private members | Need only serialization | Allow missing values when de-serializing | macro |
|------------------------------------------------------------------|------------------------------------------------------------------|------------------------------------------------------------------|-------------------------------------------------------|
| <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | **NLOHMANN_DEFINE_TYPE_INTRUSIVE** |
| <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | **NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT** |
| <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: grey;">:octicons-skip-fill-24:</div> | **NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE** |
## Parameters
`type` (in)
: name of the type (class, struct) to serialize/deserialize
`member` (in)
: name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
## Default definition
The macros add two friend functions to the class which take care of the serialization and deserialization:
```cpp
template<typename BasicJsonType>
friend void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
friend void from_json(const BasicJsonType&, type&); // except (3)
```
See the examples below for the concrete generated code.
## Notes
!!! info "Prerequisites"
1. The type `type` must be default constructible (except (3)). See [How can I use `get()` for non-default
constructible/non-copyable types?][GetNonDefNonCopy] for how to overcome this limitation.
2. The macro must be used inside the type (class/struct).
[GetNonDefNonCopy]: ../../features/arbitrary_types.md#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
!!! warning "Implementation limits"
- The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types
with more than 63 member variables, you need to define the `to_json`/`from_json` functions manually.
## Examples
??? example "Example (1): NLOHMANN_DEFINE_TYPE_INTRUSIVE"
Consider the following complete example:
```cpp hl_lines="22"
--8<-- "examples/nlohmann_define_type_intrusive_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_intrusive_macro.output"
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has private member variables. This makes `NLOHMANN_DEFINE_TYPE_INTRUSIVE` applicable, but not
`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`.
- The macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is used _inside_ the class.
- A missing key "age" in the deserialization yields an exception. To fall back to the default value,
`NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` can be used.
The macro is equivalent to:
```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34 35 36"
--8<-- "examples/nlohmann_define_type_intrusive_explicit.cpp"
```
??? example "Example (2): NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT"
Consider the following complete example:
```cpp hl_lines="22"
--8<-- "examples/nlohmann_define_type_intrusive_with_default_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_intrusive_with_default_macro.output"
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has private member variables. This makes `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` applicable,
but not `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`.
- The macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` is used _inside_ the class.
- A missing key "age" in the deserialization does not yield an exception. Instead, the default value `-1` is used.
The macro is equivalent to:
```cpp hl_lines="22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37"
--8<-- "examples/nlohmann_define_type_intrusive_with_default_explicit.cpp"
```
Note how a default-initialized `person` object is used in the `from_json` to fill missing values.
??? example "Example (3): NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE"
Consider the following complete example:
```cpp hl_lines="22"
--8<-- "examples/nlohmann_define_type_intrusive_only_serialize_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_intrusive_only_serialize_macro.output"
```
Notes:
- `ns::person` is non-default-constructible. This allows this macro to be used instead of
`NLOHMANN_DEFINE_TYPE_INTRUSIVE` and `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT`.
- `ns::person` has private member variables. This makes `NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE` applicable, but not
`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE`.
- The macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE` is used _inside_ the class.
The macro is equivalent to:
```cpp hl_lines="22 22 23 24 25 26 27 28"
--8<-- "examples/nlohmann_define_type_intrusive_only_serialize_explicit.cpp"
```
## See also
- [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](nlohmann_define_type_non_intrusive.md)
for a similar macro that can be defined _outside_ the type.
- [NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE,
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](nlohmann_define_derived_type.md) for similar macros for
derived types
- [Arbitrary Type Conversions](../../features/arbitrary_types.md) for an overview.
## Version history
1. Added in version 3.9.0.
2. Added in version 3.11.0.
3. Added in version 3.11.3.
@@ -291,4 +291,4 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;serialization: &quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>outside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_non_intrusive/ >NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>outside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,424 @@
# NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE
```
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...) // (1)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...) // (2)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, member...) // (3)
```
These macros can be used to simplify the serialization/deserialization of types if you want to use a JSON object as serialization and want to use the member variable names as object keys in that object. The macro is to be defined **inside** the class/struct to create code for. Unlike [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md), it can access private members. The first parameter is the name of the class/struct, and all remaining parameters name the members.
1. Will use [`at`](https://json.nlohmann.me/api/basic_json/at/index.md) during deserialization and will throw [`out_of_range.403`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range403) if a key is missing in the JSON object.
1. Will use [`value`](https://json.nlohmann.me/api/basic_json/value/index.md) during deserialization and fall back to the default value for the respective type of the member variable if a key in the JSON object is missing. The generated `from_json()` function default constructs an object and uses its values as the defaults when calling the `value` function.
1. Only defines the serialization. Useful in cases when the type does not have a default constructor and only serialization is required.
Summary:
| Need access to private members | Need only serialization | Allow missing values when de-serializing | macro |
| ------------------------------ | ----------------------- | ---------------------------------------- | ------------------------------------------------- |
| | | | **NLOHMANN_DEFINE_TYPE_INTRUSIVE** |
| | | | **NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT** |
| | | | **NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE** |
## Parameters
`type` (in) : name of the type (class, struct) to serialize/deserialize
`member` (in) : name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
## Default definition
The macros add two friend functions to the class which take care of the serialization and deserialization:
```
template<typename BasicJsonType>
friend void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
friend void from_json(const BasicJsonType&, type&); // except (3)
```
See the examples below for the concrete generated code.
## Notes
Prerequisites
1. The type `type` must be default constructible (except (3)). See [How can I use `get()` for non-default constructible/non-copyable types?](https://json.nlohmann.me/features/arbitrary_types/#how-can-i-use-get-for-non-default-constructiblenon-copyable-types) for how to overcome this limitation.
1. The macro must be used inside the type (class/struct).
Implementation limits
- The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the `to_json`/`from_json` functions manually.
## Examples
Example (1): NLOHMANN_DEFINE_TYPE_INTRUSIVE
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
class person
{
private:
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
public:
person() = default;
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
NLOHMANN_DEFINE_TYPE_INTRUSIVE(person, name, address, age)
};
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
try
{
auto p3 = j3.get<ns::person>();
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
}
```
Output:
```
serialization: {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
deserialization failed: [json.exception.out_of_range.403] key 'age' not found
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has private member variables. This makes `NLOHMANN_DEFINE_TYPE_INTRUSIVE` applicable, but not `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`.
- The macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE` is used *inside* the class.
- A missing key "age" in the deserialization yields an exception. To fall back to the default value, `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` can be used.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
class person
{
private:
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
public:
person() = default;
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
template<typename BasicJsonType>
friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["name"] = nlohmann_json_t.name;
nlohmann_json_j["address"] = nlohmann_json_t.address;
nlohmann_json_j["age"] = nlohmann_json_t.age;
}
template<typename BasicJsonType>
friend void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
{
nlohmann_json_t.name = nlohmann_json_j.at("name");
nlohmann_json_t.address = nlohmann_json_j.at("address");
nlohmann_json_t.age = nlohmann_json_j.at("age");
}
};
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
try
{
auto p3 = j3.get<ns::person>();
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
}
```
Example (2): NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
class person
{
private:
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
public:
person() = default;
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(person, name, address, age)
};
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
}
```
Output:
```
serialization: {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
roundtrip: {"address":"742 Evergreen Terrace","age":-1,"name":"Maggie Simpson"}
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has private member variables. This makes `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` applicable, but not `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`.
- The macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT` is used *inside* the class.
- A missing key "age" in the deserialization does not yield an exception. Instead, the default value `-1` is used.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
class person
{
private:
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
public:
person() = default;
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
template<typename BasicJsonType>
friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["name"] = nlohmann_json_t.name;
nlohmann_json_j["address"] = nlohmann_json_t.address;
nlohmann_json_j["age"] = nlohmann_json_t.age;
}
template<typename BasicJsonType>
friend void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
{
person nlohmann_json_default_obj;
nlohmann_json_t.name = nlohmann_json_j.value("name", nlohmann_json_default_obj.name);
nlohmann_json_t.address = nlohmann_json_j.value("address", nlohmann_json_default_obj.address);
nlohmann_json_t.age = nlohmann_json_j.value("age", nlohmann_json_default_obj.age);
}
};
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
}
```
Note how a default-initialized `person` object is used in the `from_json` to fill missing values.
Example (3): NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
class person
{
private:
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
public:
// No default constructor
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
NLOHMANN_DEFINE_TYPE_INTRUSIVE(person, name, address, age)
};
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
}
```
Output:
```
serialization: {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
```
Notes:
- `ns::person` is non-default-constructible. This allows this macro to be used instead of `NLOHMANN_DEFINE_TYPE_INTRUSIVE` and `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT`.
- `ns::person` has private member variables. This makes `NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE` applicable, but not `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE`.
- The macro `NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE` is used *inside* the class.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
class person
{
private:
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
public:
// No default constructor
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
template<typename BasicJsonType>
friend void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["name"] = nlohmann_json_t.name;
nlohmann_json_j["address"] = nlohmann_json_t.address;
nlohmann_json_j["age"] = nlohmann_json_t.age;
}
};
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
}
```
## See also
- [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/index.md) for a similar macro that can be defined *outside* the type.
- [NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) for similar macros for derived types
- [Arbitrary Type Conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) for an overview.
## Version history
1. Added in version 3.9.0.
1. Added in version 3.11.0.
1. Added in version 3.11.3.
@@ -0,0 +1,171 @@
# NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE
```cpp
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...) // (1)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...) // (2)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, member...) // (3)
```
These macros can be used to simplify the serialization/deserialization of types if you want to use a JSON object as
serialization and want to use the member variable names as object keys in that object. The macro is to be defined
**outside** the class/struct to create code for, but **inside** its namespace. Unlike
[`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](nlohmann_define_type_intrusive.md), it **cannot** access private members. The first
parameter is the name of the class/struct, and all remaining parameters name the members.
1. Will use [`at`](../basic_json/at.md) during deserialization and will throw
[`out_of_range.403`](../../home/exceptions.md#jsonexceptionout_of_range403) if a key is missing in the JSON object.
2. Will use [`value`](../basic_json/value.md) during deserialization and fall back to the default value for the
respective type of the member variable if a key in the JSON object is missing. The generated `from_json()` function
default constructs an object and uses its values as the defaults when calling the `value` function.
3. Only defines the serialization. Useful in cases when the type does not have a default constructor and only serialization is required.
Summary:
| Need access to private members | Need only serialization | Allow missing values when de-serializing | macro |
|------------------------------------------------------------------|------------------------------------------------------------------|------------------------------------------------------------------|-------------------------------------------------------|
| <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | **NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE** |
| <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | **NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT** |
| <div style="color: red;">:octicons-x-circle-fill-24:</div> | <div style="color: green;">:octicons-check-circle-fill-24:</div> | <div style="color: grey;">:octicons-skip-fill-24:</div> | **NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE** |
## Parameters
`type` (in)
: name of the type (class, struct) to serialize/deserialize
`member` (in)
: name of the (public) member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
## Default definition
The macros add two functions to the namespace which take care of the serialization and deserialization:
```cpp
template<typename BasicJsonType>
void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
void from_json(const BasicJsonType&, type&); // except (3)
```
See the examples below for the concrete generated code.
## Notes
!!! info "Prerequisites"
1. The type `type` must be default constructible (except (3). See [How can I use `get()` for non-default constructible/non-copyable types?][GetNonDefNonCopy]
for how to overcome this limitation.
2. The macro must be used outside the type (class/struct).
3. The passed members must be public.
[GetNonDefNonCopy]: ../../features/arbitrary_types.md#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
!!! warning "Implementation limits"
- The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types
with more than 63 member variables, you need to define the `to_json`/`from_json` functions manually.
## Examples
??? example "Example (1): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE"
Consider the following complete example:
```cpp hl_lines="16"
--8<-- "examples/nlohmann_define_type_non_intrusive_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_non_intrusive_macro.output"
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` is used _outside_ the class, but _inside_ its namespace `ns`.
- A missing key "age" in the deserialization yields an exception. To fall back to the default value,
`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT` can be used.
The macro is equivalent to:
```cpp hl_lines="16 17 18 19 20 21 22 23 24 25 26 27 28 29 30"
--8<-- "examples/nlohmann_define_type_non_intrusive_explicit.cpp"
```
??? example "Example (2): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT"
Consider the following complete example:
```cpp hl_lines="21"
--8<-- "examples/nlohmann_define_type_non_intrusive_with_default_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_non_intrusive_with_default_macro.output"
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`
applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT` is used _outside_ the class, but _inside_ its
namespace `ns`.
- A missing key "age" in the deserialization does not yield an exception. Instead, the default value `-1` is used.
The macro is equivalent to:
```cpp hl_lines="21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36"
--8<-- "examples/nlohmann_define_type_non_intrusive_with_default_explicit.cpp"
```
Note how a default-initialized `person` object is used in the `from_json` to fill missing values.
??? example "Example (3): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE"
Consider the following complete example:
```cpp hl_lines="16"
--8<-- "examples/nlohmann_define_type_non_intrusive_only_serialize_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_non_intrusive_only_serialize_macro.output"
```
Notes:
- `ns::person` is non-default-constructible. This allows this macro to be used instead of
`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` and `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE` is used _outside_ the class, but _inside_ its namespace `ns`.
The macro is equivalent to:
```cpp hl_lines="16 17 18 19 20 21 22"
--8<-- "examples/nlohmann_define_type_non_intrusive_only_serialize_explicit.cpp"
```
## See also
- [NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE](nlohmann_define_type_intrusive.md)
for a similar macro that can be defined _inside_ the type.
- [NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE,
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT,
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](nlohmann_define_derived_type.md) for similar macros for
derived types
- [Arbitrary Type Conversions](../../features/arbitrary_types.md) for an overview.
## Version history
1. Added in version 3.9.0.
2. Added in version 3.11.0.
3. Added in version 3.11.3.
@@ -259,4 +259,4 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;serialization: &quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>inside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_define_type_intrusive/ >NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE</a> for a similar macro that can be defined <em>inside</em> the type.</li> <li><a href=../nlohmann_define_derived_type/ >NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE</a> for similar macros for derived types</li> <li><a href=../../../features/arbitrary_types/ >Arbitrary Type Conversions</a> for an overview.</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.9.0.</li> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.3.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,393 @@
# NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE
```
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...) // (1)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...) // (2)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, member...) // (3)
```
These macros can be used to simplify the serialization/deserialization of types if you want to use a JSON object as serialization and want to use the member variable names as object keys in that object. The macro is to be defined **outside** the class/struct to create code for, but **inside** its namespace. Unlike [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md), it **cannot** access private members. The first parameter is the name of the class/struct, and all remaining parameters name the members.
1. Will use [`at`](https://json.nlohmann.me/api/basic_json/at/index.md) during deserialization and will throw [`out_of_range.403`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range403) if a key is missing in the JSON object.
1. Will use [`value`](https://json.nlohmann.me/api/basic_json/value/index.md) during deserialization and fall back to the default value for the respective type of the member variable if a key in the JSON object is missing. The generated `from_json()` function default constructs an object and uses its values as the defaults when calling the `value` function.
1. Only defines the serialization. Useful in cases when the type does not have a default constructor and only serialization is required.
Summary:
| Need access to private members | Need only serialization | Allow missing values when de-serializing | macro |
| ------------------------------ | ----------------------- | ---------------------------------------- | ----------------------------------------------------- |
| | | | **NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE** |
| | | | **NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT** |
| | | | **NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE** |
## Parameters
`type` (in) : name of the type (class, struct) to serialize/deserialize
`member` (in) : name of the (public) member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
## Default definition
The macros add two functions to the namespace which take care of the serialization and deserialization:
```
template<typename BasicJsonType>
void to_json(BasicJsonType&, const type&);
template<typename BasicJsonType>
void from_json(const BasicJsonType&, type&); // except (3)
```
See the examples below for the concrete generated code.
## Notes
Prerequisites
1. The type `type` must be default constructible (except (3). See [How can I use `get()` for non-default constructible/non-copyable types?](https://json.nlohmann.me/features/arbitrary_types/#how-can-i-use-get-for-non-default-constructiblenon-copyable-types) for how to overcome this limitation.
1. The macro must be used outside the type (class/struct).
1. The passed members must be public.
Implementation limits
- The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types with more than 63 member variables, you need to define the `to_json`/`from_json` functions manually.
## Examples
Example (1): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name;
std::string address;
int age;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age)
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
try
{
auto p3 = j3.get<ns::person>();
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
}
```
Output:
```
serialization: {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
deserialization failed: [json.exception.out_of_range.403] key 'age' not found
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` is used *outside* the class, but *inside* its namespace `ns`.
- A missing key "age" in the deserialization yields an exception. To fall back to the default value, `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT` can be used.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name;
std::string address;
int age;
};
template<typename BasicJsonType>
void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["name"] = nlohmann_json_t.name;
nlohmann_json_j["address"] = nlohmann_json_t.address;
nlohmann_json_j["age"] = nlohmann_json_t.age;
}
template<typename BasicJsonType>
void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
{
nlohmann_json_t.name = nlohmann_json_j.at("name");
nlohmann_json_t.address = nlohmann_json_j.at("address");
nlohmann_json_t.age = nlohmann_json_j.at("age");
}
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
try
{
auto p3 = j3.get<ns::person>();
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
}
```
Example (2): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
person() = default;
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(person, name, address, age)
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
}
```
Output:
```
serialization: {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
roundtrip: {"address":"742 Evergreen Terrace","age":-1,"name":"Maggie Simpson"}
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT` is used *outside* the class, but *inside* its namespace `ns`.
- A missing key "age" in the deserialization does not yield an exception. Instead, the default value `-1` is used.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name = "John Doe";
std::string address = "123 Fake St";
int age = -1;
person() = default;
person(std::string name_, std::string address_, int age_)
: name(std::move(name_)), address(std::move(address_)), age(age_)
{}
};
template<typename BasicJsonType>
void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["name"] = nlohmann_json_t.name;
nlohmann_json_j["address"] = nlohmann_json_t.address;
nlohmann_json_j["age"] = nlohmann_json_t.age;
}
template<typename BasicJsonType>
void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
{
person nlohmann_json_default_obj;
nlohmann_json_t.name = nlohmann_json_j.value("name", nlohmann_json_default_obj.name);
nlohmann_json_t.address = nlohmann_json_j.value("address", nlohmann_json_default_obj.address);
nlohmann_json_t.age = nlohmann_json_j.value("age", nlohmann_json_default_obj.age);
}
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"address": "742 Evergreen Terrace", "age": 40, "name": "Homer Simpson"})"_json;
auto p2 = j2.get<ns::person>();
// incomplete deserialization:
json j3 = R"({"address": "742 Evergreen Terrace", "name": "Maggie Simpson"})"_json;
auto p3 = j3.get<ns::person>();
std::cout << "roundtrip: " << json(p3) << std::endl;
}
```
Note how a default-initialized `person` object is used in the `from_json` to fill missing values.
Example (3): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name;
std::string address;
int age;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(person, name, address, age)
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
}
```
Output:
```
serialization: {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
```
Notes:
- `ns::person` is non-default-constructible. This allows this macro to be used instead of `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE` and `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE` is used *outside* the class, but *inside* its namespace `ns`.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name;
std::string address;
int age;
};
template<typename BasicJsonType>
void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["name"] = nlohmann_json_t.name;
nlohmann_json_j["address"] = nlohmann_json_t.address;
nlohmann_json_j["age"] = nlohmann_json_t.age;
}
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
}
```
## See also
- [NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE](https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/index.md) for a similar macro that can be defined *inside* the type.
- [NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE](https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/index.md) for similar macros for derived types
- [Arbitrary Type Conversions](https://json.nlohmann.me/features/arbitrary_types/index.md) for an overview.
## Version history
1. Added in version 3.9.0.
1. Added in version 3.11.0.
1. Added in version 3.11.3.
@@ -0,0 +1,78 @@
<h1>NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES,
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES,
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES,
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES,
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES,
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES</h1>
```cpp
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, base_type, "json_member_name", member...)
```
These macros can be used in case you want to use the custom names for the member variables in the resulting JSON.
They behave exactly as their non-`WITH_NAMES` counterparts, but require an additional parameter for each member variable
which will be used in JSON. Both serialization and deserialization will only use the custom names for JSON, the names of
the member variables themselves will be ignored.
Using the named conversion macros will halve the maximum number of member variables from 63 to 31.
For further information please refer to the corresponding macros without `WITH_NAMES`.
## Parameters
`type` (in)
: name of the type (class, struct) to serialize/deserialize
`base_type` (in)
: name of the base type (class, struct) `type` is derived from (used only in `DEFINE_DERIVED_TYPE` macros)
`json_member_name` (in)
: the string that will be used as the name for the next value
`member` (in)
: name of the member variable to serialize/deserialize
## Examples
??? example "Example (1): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES"
Consider the following complete example:
```cpp hl_lines="16"
--8<-- "examples/nlohmann_define_type_non_intrusive_with_names_macro.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_define_type_non_intrusive_with_names_macro.output"
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES` is used _outside_ the class, but _inside_ its namespace `ns`.
- A missing key "age" in the deserialization yields an exception. To fall back to the default value,
`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES` can be used.
The macro is equivalent to:
```cpp hl_lines="16 17 18 19 20 21 22 23 24 25 26 27 28"
--8<-- "examples/nlohmann_define_type_non_intrusive_with_names_explicit.cpp"
```
## Version history
1. Added in version 3.12.x.
@@ -108,4 +108,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>&quot;deserialization failed: &quot;</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.12.x.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.12.x.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M162.7 210c-1.8 3.3-25.2 44.4-70.1 123.5-4.9 8.3-10.8 12.5-17.7 12.5H9.8c-7.7 0-12.1-7.5-8.5-14.4l69-121.3q.3 0 0-.3l-43.9-75.6c-4.3-7.8.3-14.Line truncated
@@ -0,0 +1,160 @@
# NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES
```
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(type, base_type, "json_member_name", member...)
#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(type, base_type, "json_member_name", member...)
```
These macros can be used in case you want to use the custom names for the member variables in the resulting JSON. They behave exactly as their non-`WITH_NAMES` counterparts, but require an additional parameter for each member variable which will be used in JSON. Both serialization and deserialization will only use the custom names for JSON, the names of the member variables themselves will be ignored.
Using the named conversion macros will halve the maximum number of member variables from 63 to 31.
For further information please refer to the corresponding macros without `WITH_NAMES`.
## Parameters
`type` (in) : name of the type (class, struct) to serialize/deserialize
`base_type` (in) : name of the base type (class, struct) `type` is derived from (used only in `DEFINE_DERIVED_TYPE` macros)
`json_member_name` (in) : the string that will be used as the name for the next value
`member` (in) : name of the member variable to serialize/deserialize
## Examples
Example (1): NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES
Consider the following complete example:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name;
std::string address;
int age;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(person, "json_name", name, "json_address", address, "json_age", age)
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"})"_json;
auto p2 = j2.template get<ns::person>();
// incomplete deserialization:
json j3 = R"({"json_address": "742 Evergreen Terrace", "json_name": "Maggie Simpson"})"_json;
try
{
auto p3 = j3.template get<ns::person>();
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
}
```
Output:
```
serialization: {"json_address":"744 Evergreen Terrace","json_age":60,"json_name":"Ned Flanders"}
deserialization failed: [json.exception.out_of_range.403] key 'json_age' not found
```
Notes:
- `ns::person` is default-constructible. This is a requirement for using the macro.
- `ns::person` has only public member variables. This makes `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES` applicable.
- The macro `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES` is used *outside* the class, but *inside* its namespace `ns`.
- A missing key "age" in the deserialization yields an exception. To fall back to the default value, `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES` can be used.
The macro is equivalent to:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
namespace ns
{
struct person
{
std::string name;
std::string address;
int age;
};
template <typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0>
void to_json(BasicJsonType& nlohmann_json_j, const person& nlohmann_json_t)
{
nlohmann_json_j["json_name"] = nlohmann_json_t.name;
nlohmann_json_j["json_address"] = nlohmann_json_t.address;
nlohmann_json_j["json_age"] = nlohmann_json_t.age;
}
template <typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0>
void from_json(const BasicJsonType& nlohmann_json_j, person& nlohmann_json_t)
{
nlohmann_json_j.at("json_name").get_to(nlohmann_json_t.name);
nlohmann_json_j.at("json_address").get_to(nlohmann_json_t.address);
nlohmann_json_j.at("json_age").get_to(nlohmann_json_t.age);
}
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
// serialization: person -> json
json j = p;
std::cout << "serialization: " << j << std::endl;
// deserialization: json -> person
json j2 = R"({"json_address": "742 Evergreen Terrace", "json_age": 40, "json_name": "Homer Simpson"})"_json;
auto p2 = j2.template get<ns::person>();
// incomplete deserialization:
json j3 = R"({"json_address": "742 Evergreen Terrace", "json_name": "Maggie Simpson"})"_json;
try
{
auto p3 = j3.template get<ns::person>();
}
catch (const json::exception& e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
}
```
## Version history
1. Added in version 3.12.x.
+41
View File
@@ -0,0 +1,41 @@
# NLOHMANN_JSON_NAMESPACE
```cpp
#define NLOHMANN_JSON_NAMESPACE /* value */
```
This macro evaluates to the full name of the `nlohmann` namespace.
## Default definition
The default value consists of the root namespace (`nlohmann`) and an inline ABI namespace. See
[`nlohmann` Namespace](../../features/namespace.md#structure) for details.
When the macro is not defined, the library will define it to its default value. Overriding this value has no effect on
the library.
## Examples
??? example
The example shows how to use `NLOHMANN_JSON_NAMESPACE` instead of just `nlohmann`, as well as how to output the value
of `NLOHMANN_JSON_NAMESPACE`.
```cpp
--8<-- "examples/nlohmann_json_namespace.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_namespace.output"
```
## See also
- [`NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END`](nlohmann_json_namespace_begin.md)
- [`NLOHMANN_JSON_NAMESPACE_NO_VERSION`](nlohmann_json_namespace_no_version.md)
## Version history
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2.
@@ -14,4 +14,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>QUOTE</span><span class=p>(</span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>nl</span><span class=err>ohma</span><span class=kc>nn</span><span class=p>::</span><span class=err>jso</span><span class=kc>n</span><span class=err>_abi_v</span><span class=mi>3</span><span class=err>_</span><span class=mi>12</span><span class=err>_</span><span class=mi>0</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.Line truncated
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.Line truncated
@@ -0,0 +1,51 @@
# NLOHMANN_JSON_NAMESPACE
```
#define NLOHMANN_JSON_NAMESPACE /* value */
```
This macro evaluates to the full name of the `nlohmann` namespace.
## Default definition
The default value consists of the root namespace (`nlohmann`) and an inline ABI namespace. See [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/#structure) for details.
When the macro is not defined, the library will define it to its default value. Overriding this value has no effect on the library.
## Examples
Example
The example shows how to use `NLOHMANN_JSON_NAMESPACE` instead of just `nlohmann`, as well as how to output the value of `NLOHMANN_JSON_NAMESPACE`.
```
#include <iostream>
#include <nlohmann/json.hpp>
// possible use case: use NLOHMANN_JSON_NAMESPACE instead of nlohmann
using json = NLOHMANN_JSON_NAMESPACE::json;
// macro needed to output the NLOHMANN_JSON_NAMESPACE as string literal
#define Q(x) #x
#define QUOTE(x) Q(x)
int main()
{
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << std::endl;
}
```
Output:
```
nlohmann::json_abi_v3_12_0
```
## See also
- [`NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END`](https://json.nlohmann.me/api/macros/nlohmann_json_namespace_begin/index.md)
- [`NLOHMANN_JSON_NAMESPACE_NO_VERSION`](https://json.nlohmann.me/api/macros/nlohmann_json_namespace_no_version/index.md)
## Version history
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2.
@@ -0,0 +1,61 @@
# NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END
```cpp
#define NLOHMANN_JSON_NAMESPACE_BEGIN /* value */ // (1)
#define NLOHMANN_JSON_NAMESPACE_END /* value */ // (2)
```
These macros can be used to open and close the `nlohmann` namespace. See
[`nlohmann` Namespace](../../features/namespace.md#structure) for details.
1. Opens the namespace.
2. Closes the namespace.
## Default definition
The default definitions open and close the `nlohmann` namespace. The precise definition of
[`NLOHMANN_JSON_NAMESPACE_BEGIN`] varies as described [here](../../features/namespace.md#structure).
1. Default definition of `NLOHMANN_JSON_NAMESPACE_BEGIN`:
```cpp
namespace nlohmann
{
inline namespace json_abi_v3_12_0
{
```
2. Default definition of `NLOHMANN_JSON_NAMESPACE_END`:
```cpp
} // namespace json_abi_v3_12_0
} // namespace nlohmann
```
When these macros are not defined, the library will define them to their default definitions.
## Examples
??? example
The example shows how to use `NLOHMANN_JSON_NAMESPACE_BEGIN`/`NLOHMANN_JSON_NAMESPACE_END` from the
[How do I convert third-party types?](../../features/arbitrary_types.md#how-do-i-convert-third-party-types) page.
```cpp
--8<-- "examples/nlohmann_json_namespace_begin.c++17.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_namespace_begin.c++17.output"
```
## See also
- [`nlohmann` Namespace](../../features/namespace.md)
- [NLOHMANN_JSON_NAMESPACE](nlohmann_json_namespace.md)
- [`NLOHMANN_JSON_NAMESPACE_NO_VERSION`](nlohmann_json_namespace_no_version.md)
## Version history
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2.
@@ -40,4 +40,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>[</span><span class=mi>1</span><span class=p>,</span><span class=kc>null</span><span class=p>]</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/namespace/ ><code>nlohmann</code> Namespace</a></li> <li><a href=../nlohmann_json_namespace/ >NLOHMANN_JSON_NAMESPACE</a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__linLine truncated
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/namespace/ ><code>nlohmann</code> Namespace</a></li> <li><a href=../nlohmann_json_namespace/ >NLOHMANN_JSON_NAMESPACE</a></li> <li><a href=../nlohmann_json_namespace_no_version/ ><code>NLOHMANN_JSON_NAMESPACE_NO_VERSION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.0. Changed inline namespace name in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__linLine truncated
@@ -0,0 +1,91 @@
# NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END
```
#define NLOHMANN_JSON_NAMESPACE_BEGIN /* value */ // (1)
#define NLOHMANN_JSON_NAMESPACE_END /* value */ // (2)
```
These macros can be used to open and close the `nlohmann` namespace. See [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/#structure) for details.
1. Opens the namespace.
1. Closes the namespace.
## Default definition
The default definitions open and close the `nlohmann` namespace. The precise definition of \[`NLOHMANN_JSON_NAMESPACE_BEGIN`\] varies as described [here](https://json.nlohmann.me/features/namespace/#structure).
1. Default definition of `NLOHMANN_JSON_NAMESPACE_BEGIN`:
```
namespace nlohmann
{
inline namespace json_abi_v3_12_0
{
```
1. Default definition of `NLOHMANN_JSON_NAMESPACE_END`:
```
} // namespace json_abi_v3_12_0
} // namespace nlohmann
```
When these macros are not defined, the library will define them to their default definitions.
## Examples
Example
The example shows how to use `NLOHMANN_JSON_NAMESPACE_BEGIN`/`NLOHMANN_JSON_NAMESPACE_END` from the [How do I convert third-party types?](https://json.nlohmann.me/features/arbitrary_types/#how-do-i-convert-third-party-types) page.
```
#include <iostream>
#include <optional>
#include <nlohmann/json.hpp>
// partial specialization (see https://json.nlohmann.me/features/arbitrary_types/)
NLOHMANN_JSON_NAMESPACE_BEGIN
template <typename T>
struct adl_serializer<std::optional<T>>
{
static void to_json(json& j, const std::optional<T>& opt)
{
if (opt == std::nullopt)
{
j = nullptr;
}
else
{
j = *opt;
}
}
};
NLOHMANN_JSON_NAMESPACE_END
int main()
{
std::optional<int> o1 = 1;
std::optional<int> o2 = std::nullopt;
NLOHMANN_JSON_NAMESPACE::json j;
j.push_back(o1);
j.push_back(o2);
std::cout << j << std::endl;
}
```
Output:
```
[1,null]
```
## See also
- [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/index.md)
- [NLOHMANN_JSON_NAMESPACE](https://json.nlohmann.me/api/macros/nlohmann_json_namespace/index.md)
- [`NLOHMANN_JSON_NAMESPACE_NO_VERSION`](https://json.nlohmann.me/api/macros/nlohmann_json_namespace_no_version/index.md)
## Version history
- Added in version 3.11.0. Changed inline namespace name in version 3.11.2.
@@ -0,0 +1,45 @@
# NLOHMANN_JSON_NAMESPACE_NO_VERSION
```cpp
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION /* value */
```
If defined to `1`, the version component is omitted from the inline namespace. See
[`nlohmann` Namespace](../../features/namespace.md#structure) for details.
## Default definition
The default value is `0`.
```cpp
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
```
When the macro is not defined, the library will define it to its default value.
## Examples
??? example
The example shows how to use `NLOHMANN_JSON_NAMESPACE_NO_VERSION` to disable the version component of the inline
namespace.
```cpp
--8<-- "examples/nlohmann_json_namespace_no_version.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_namespace_no_version.output"
```
## See also
- [`nlohmann` Namespace](../../features/namespace.md)
- [`NLOHMANN_JSON_NAMESPACE`](nlohmann_json_namespace.md)
- [`NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END`](nlohmann_json_namespace_begin.md)
## Version history
- Added in version 3.11.2.
@@ -14,4 +14,4 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>QUOTE</span><span class=p>(</span><span class=n>NLOHMANN_JSON_NAMESPACE</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>nl</span><span class=err>ohma</span><span class=kc>nn</span><span class=p>::</span><span class=err>jso</span><span class=kc>n</span><span class=err>_abi</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/namespace/ ><code>nlohmann</code> Namespace</a></li> <li><a href=../nlohmann_json_namespace/ ><code>NLOHMANN_JSON_NAMESPACE</code></a></li> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/namespace/ ><code>nlohmann</code> Namespace</a></li> <li><a href=../nlohmann_json_namespace/ ><code>NLOHMANN_JSON_NAMESPACE</code></a></li> <li><a href=../nlohmann_json_namespace_begin/ ><code>NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.11.2.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,55 @@
# NLOHMANN_JSON_NAMESPACE_NO_VERSION
```
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION /* value */
```
If defined to `1`, the version component is omitted from the inline namespace. See [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/#structure) for details.
## Default definition
The default value is `0`.
```
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
```
When the macro is not defined, the library will define it to its default value.
## Examples
Example
The example shows how to use `NLOHMANN_JSON_NAMESPACE_NO_VERSION` to disable the version component of the inline namespace.
```
#include <iostream>
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 1
#include <nlohmann/json.hpp>
// macro needed to output the NLOHMANN_JSON_NAMESPACE as string literal
#define Q(x) #x
#define QUOTE(x) Q(x)
int main()
{
std::cout << QUOTE(NLOHMANN_JSON_NAMESPACE) << std::endl;
}
```
Output:
```
nlohmann::json_abi
```
## See also
- [`nlohmann` Namespace](https://json.nlohmann.me/features/namespace/index.md)
- [`NLOHMANN_JSON_NAMESPACE`](https://json.nlohmann.me/api/macros/nlohmann_json_namespace/index.md)
- [`NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END`](https://json.nlohmann.me/api/macros/nlohmann_json_namespace_begin/index.md)
## Version history
- Added in version 3.11.2.
@@ -0,0 +1,86 @@
# NLOHMANN_JSON_SERIALIZE_ENUM
```cpp
#define NLOHMANN_JSON_SERIALIZE_ENUM(type, conversion...)
```
By default, enum values are serialized to JSON as integers. In some cases, this could result in undesired behavior. If
an enum is modified or re-ordered after data has been serialized to JSON, the later deserialized JSON data may be
undefined or a different enum value than was originally intended.
The `NLOHMANN_JSON_SERIALIZE_ENUM` allows to define a user-defined serialization for every enumerator.
## Parameters
`type` (in)
: name of the enum to serialize/deserialize
`conversion` (in)
: a pair of an enumerator and a JSON serialization; arbitrary pairs can be given as a comma-separated list
## Default definition
The macro adds two functions to the namespace which take care of the serialization and deserialization:
```cpp
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const type& e);
template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, type& e);
```
## Notes
!!! info "Prerequisites"
The macro must be used inside the namespace of the enum.
!!! important "Important notes"
- When using [`get<ENUM_TYPE>()`](../basic_json/get.md), undefined JSON values will default to the first specified
conversion. Select this default pair carefully. See example 1 below.
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
list will be returned when converting to or from JSON. See example 2 below.
## Examples
??? example "Example 1: Basic usage"
The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM` can be used to serialize/deserialize both classical enums and
C++11 enum classes:
```cpp hl_lines="16 17 18 19 20 21 22 29 30 31 32 33"
--8<-- "examples/nlohmann_json_serialize_enum.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum.output"
```
??? example "Example 2: Multiple conversions for one enumerator"
The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always
be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an
alternative *deserialization* from `"rot"` to `Color::red`.
```cpp hl_lines="17"
--8<-- "examples/nlohmann_json_serialize_enum_2.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_2.output"
```
## See also
- [Specializing enum conversion](../../features/enum_conversion.md)
- [`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](./nlohmann_json_serialize_enum_strict.md)
- [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
## Version history
Added in version 3.4.0.
@@ -101,4 +101,4 @@
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>0</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=s2>&quot;red&quot;</span>
<span class=s2>&quot;rot&quot;</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>0</span>
<span class=s2>&quot;red&quot;</span><span class=w> </span><span class=mi>-</span><span class=err>&gt;</span><span class=w> </span><span class=mi>0</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.4.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.4.0.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,171 @@
# NLOHMANN_JSON_SERIALIZE_ENUM
```
#define NLOHMANN_JSON_SERIALIZE_ENUM(type, conversion...)
```
By default, enum values are serialized to JSON as integers. In some cases, this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later deserialized JSON data may be undefined or a different enum value than was originally intended.
The `NLOHMANN_JSON_SERIALIZE_ENUM` allows to define a user-defined serialization for every enumerator.
## Parameters
`type` (in) : name of the enum to serialize/deserialize
`conversion` (in) : a pair of an enumerator and a JSON serialization; arbitrary pairs can be given as a comma-separated list
## Default definition
The macro adds two functions to the namespace which take care of the serialization and deserialization:
```
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const type& e);
template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, type& e);
```
## Notes
Prerequisites
The macro must be used inside the namespace of the enum.
Important notes
- When using [`get<ENUM_TYPE>()`](https://json.nlohmann.me/api/basic_json/get/index.md), undefined JSON values will default to the first specified conversion. Select this default pair carefully. See example 1 below.
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from JSON. See example 2 below.
## Examples
Example 1: Basic usage
The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM` can be used to serialize/deserialize both classical enums and C++11 enum classes:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum TaskState
{
TS_STOPPED,
TS_RUNNING,
TS_COMPLETED,
TS_INVALID = -1
};
NLOHMANN_JSON_SERIALIZE_ENUM(TaskState,
{
{ TS_INVALID, nullptr },
{ TS_STOPPED, "stopped" },
{ TS_RUNNING, "running" },
{ TS_COMPLETED, "completed" }
})
enum class Color
{
red, green, blue, unknown
};
NLOHMANN_JSON_SERIALIZE_ENUM(Color,
{
{ Color::unknown, "unknown" }, { Color::red, "red" },
{ Color::green, "green" }, { Color::blue, "blue" }
})
} // namespace ns
int main()
{
// serialization
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
// deserialization
json j_running = "running";
json j_blue = "blue";
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
// deserializing undefined JSON value to enum
// (where the first map entry above is the default)
json j_pi = 3.14;
auto invalid = j_pi.get<ns::TaskState>();
auto unknown = j_pi.get<ns::Color>();
std::cout << j_pi << " -> " << invalid << ", "
<< j_pi << " -> " << static_cast<int>(unknown) << std::endl;
}
```
Output:
```
ns::TS_STOPPED -> "stopped", ns::Color::red -> "red"
"running" -> 1, "blue" -> 2
3.14 -> -1, 3.14 -> 3
```
Example 2: Multiple conversions for one enumerator
The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an alternative *deserialization* from `"rot"` to `Color::red`.
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum class Color
{
red, green, blue, unknown
};
NLOHMANN_JSON_SERIALIZE_ENUM(Color,
{
{ Color::unknown, "unknown" }, { Color::red, "red" },
{ Color::green, "green" }, { Color::blue, "blue" },
{ Color::red, "rot" } // a second conversion for Color::red
})
}
int main()
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
}
```
Output:
```
0 -> "red"
"rot" -> 0
"red" -> 0
```
## See also
- [Specializing enum conversion](https://json.nlohmann.me/features/enum_conversion/index.md)
- [`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum_strict/index.md)
- [`JSON_DISABLE_ENUM_SERIALIZATION`](https://json.nlohmann.me/api/macros/json_disable_enum_serialization/index.md)
## Version history
Added in version 3.4.0.
@@ -0,0 +1,105 @@
# NLOHMANN_JSON_SERIALIZE_ENUM_STRICT
```cpp
#define NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(type, conversion...)
```
By default, enum values are serialized to JSON as integers. In some cases, this could result in undesired behavior. If
an enum is modified or re-ordered after data has been serialized to JSON, the later deserialized JSON data may be
undefined or a different enum value than was originally intended.
`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` allows to define a user-defined serialization for every enumerator that
throws an exception on undefined input.
## Parameters
`type` (in)
: name of the enum to serialize/deserialize
`conversion` (in)
: a pair of an enumerator and a JSON serialization; arbitrary pairs can be given as a comma-separated list
## Default definition
The macro adds two functions to the namespace which take care of the serialization and deserialization:
```cpp
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const type& e);
template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, type& e);
```
## Notes
!!! info "Prerequisites"
The macro must be used inside the namespace of the enum.
!!! important "Important notes"
- Undefined input throws [`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) in both
directions: when serializing an enum value not listed in the conversions, and when deserializing (e.g., via
[`get<ENUM_TYPE>()`](../basic_json/get.md)) a JSON value that matches no conversion; example:
`"enum value out of range for <type>"`.
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
list will be returned when converting to or from JSON. See example 2 below.
## Examples
??? example "Example 1: Basic usage"
The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` can be used to serialize/deserialize both classical enums and
C++11 enum classes:
```cpp hl_lines="16 17 18 19 20 21 22 29 30 31 32 33"
--8<-- "examples/nlohmann_json_serialize_enum_strict.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_strict.output"
```
??? example "Example 2: Multiple conversions for one enumerator"
The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always
be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an
alternative *deserialization* from `"rot"` to `Color::red`.
```cpp hl_lines="17"
--8<-- "examples/nlohmann_json_serialize_enum_strict_2.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_strict_2.output"
```
??? example "Example 3: exceptions on invalid serialization"
The example shows how an invalid serialization causes an exception to be thrown. In the example,
Color::unknown is not defined in the mapping used to call `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`
so causes an exception when used to serialize. Similarly, "what" does not refer to an enum
value so also causes an exception when deserialization is attempted.
```cpp hl_lines="14 32 33 43 44 45"
--8<-- "examples/nlohmann_json_serialize_enum_strict_err.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_strict_err.output"
```
## See also
- [Specializing enum conversion](../../features/enum_conversion.md)
- [`NLOHMANN_JSON_SERIALIZE_ENUM`](./nlohmann_json_serialize_enum.md)
- [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
## Version history
Added in version 3.12.x.
@@ -148,4 +148,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output: <div class=highlight><pre><span></span><code><span class=err>deserializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=w> </span><span class=kc>fa</span><span class=err>iled</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>410</span><span class=p>]</span><span class=w> </span><span class=err>e</span><span class=kc>nu</span><span class=err>m</span><span class=w> </span><span class=err>value</span><span class=w> </span><span class=err>ou</span><span class=kc>t</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>ra</span><span class=kc>n</span><span class=err>ge</span><span class=w> </span><span class=kc>f</span><span class=err>or</span><span class=w> </span><span class=err>Color</span>
<span class=err>deserializa</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=w> </span><span class=kc>fa</span><span class=err>iled</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>410</span><span class=p>]</span><span class=w> </span><span class=err>e</span><span class=kc>nu</span><span class=err>m</span><span class=w> </span><span class=err>value</span><span class=w> </span><span class=err>ou</span><span class=kc>t</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>ra</span><span class=kc>n</span><span class=err>ge</span><span class=w> </span><span class=kc>f</span><span class=err>or</span><span class=w> </span><span class=err>Color</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;what&quot;</span>
</code></pre></div></p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.12.x.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div></p> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../features/enum_conversion/ >Specializing enum conversion</a></li> <li><a href=../nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a></li> <li><a href=../json_disable_enum_serialization/ ><code>JSON_DISABLE_ENUM_SERIALIZATION</code></a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <p>Added in version 3.12.x.</p> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,230 @@
# NLOHMANN_JSON_SERIALIZE_ENUM_STRICT
```
#define NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(type, conversion...)
```
By default, enum values are serialized to JSON as integers. In some cases, this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later deserialized JSON data may be undefined or a different enum value than was originally intended.
`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` allows to define a user-defined serialization for every enumerator that throws an exception on undefined input.
## Parameters
`type` (in) : name of the enum to serialize/deserialize
`conversion` (in) : a pair of an enumerator and a JSON serialization; arbitrary pairs can be given as a comma-separated list
## Default definition
The macro adds two functions to the namespace which take care of the serialization and deserialization:
```
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const type& e);
template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, type& e);
```
## Notes
Prerequisites
The macro must be used inside the namespace of the enum.
Important notes
- Undefined input throws [`out_of_range.410`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range410) in both directions: when serializing an enum value not listed in the conversions, and when deserializing (e.g., via [`get<ENUM_TYPE>()`](https://json.nlohmann.me/api/basic_json/get/index.md)) a JSON value that matches no conversion; example: `"enum value out of range for <type>"`.
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the list will be returned when converting to or from JSON. See example 2 below.
## Examples
Example 1: Basic usage
The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` can be used to serialize/deserialize both classical enums and C++11 enum classes:
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum TaskState
{
TS_STOPPED,
TS_RUNNING,
TS_COMPLETED,
TS_INVALID = -1
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(TaskState,
{
{ TS_INVALID, nullptr },
{ TS_STOPPED, "stopped" },
{ TS_RUNNING, "running" },
{ TS_COMPLETED, "completed" }
})
enum class Color
{
red, green, blue, unknown
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color,
{
{ Color::unknown, "unknown" }, { Color::red, "red" },
{ Color::green, "green" }, { Color::blue, "blue" }
})
} // namespace ns
int main()
{
// serialization
json j_stopped = ns::TS_STOPPED;
json j_red = ns::Color::red;
std::cout << "ns::TS_STOPPED -> " << j_stopped
<< ", ns::Color::red -> " << j_red << std::endl;
// deserialization
json j_running = "running";
json j_blue = "blue";
auto running = j_running.get<ns::TaskState>();
auto blue = j_blue.get<ns::Color>();
std::cout << j_running << " -> " << running
<< ", " << j_blue << " -> " << static_cast<int>(blue) << std::endl;
}
```
Output:
```
ns::TS_STOPPED -> "stopped", ns::Color::red -> "red"
"running" -> 1, "blue" -> 2
```
Example 2: Multiple conversions for one enumerator
The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an alternative *deserialization* from `"rot"` to `Color::red`.
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum class Color
{
red, green, blue, unknown
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color,
{
{ Color::unknown, "unknown" }, { Color::red, "red" },
{ Color::green, "green" }, { Color::blue, "blue" },
{ Color::red, "rot" } // a second conversion for Color::red
})
}
int main()
{
// serialization
json j_red = ns::Color::red;
std::cout << static_cast<int>(ns::Color::red) << " -> " << j_red << std::endl;
// deserialization
json j_rot = "rot";
auto rot = j_rot.get<ns::Color>();
auto red = j_red.get<ns::Color>();
std::cout << j_rot << " -> " << static_cast<int>(rot) << std::endl;
std::cout << j_red << " -> " << static_cast<int>(red) << std::endl;
}
```
Output:
```
0 -> "red"
"rot" -> 0
"red" -> 0
```
Example 3: exceptions on invalid serialization
The example shows how an invalid serialization causes an exception to be thrown. In the example, Color::unknown is not defined in the mapping used to call `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` so causes an exception when used to serialize. Similarly, "what" does not refer to an enum value so also causes an exception when deserialization is attempted.
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
enum class Color
{
red,
green,
blue,
unknown // not mapped in JSON_SERIALIZE_ENUM_STRICT
};
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color,
{
{Color::red, "red"},
{Color::green, "green"},
{Color::blue, "blue"}
})
} // namespace ns
int main()
{
// invalid serialization
try
{
// ns::color::unknown was not mapped in macro
json invalid_serialization = ns::Color::unknown;
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
// invalid deserialization
try
{
// what does not map to an enum
json invalid_deserialization("what");
ns::Color color = invalid_deserialization.get<ns::Color>();
}
catch (const json::exception e)
{
std::cout << "deserialization failed: " << e.what() << std::endl;
}
return 0;
}
```
Output:
```
deserialization failed: [json.exception.out_of_range.410] enum value out of range for Color
deserialization failed: [json.exception.out_of_range.410] enum value out of range for Color: "what"
```
## See also
- [Specializing enum conversion](https://json.nlohmann.me/features/enum_conversion/index.md)
- [`NLOHMANN_JSON_SERIALIZE_ENUM`](https://json.nlohmann.me/api/macros/nlohmann_json_serialize_enum/index.md)
- [`JSON_DISABLE_ENUM_SERIALIZATION`](https://json.nlohmann.me/api/macros/json_disable_enum_serialization/index.md)
## Version history
Added in version 3.12.x.
+40
View File
@@ -0,0 +1,40 @@
# NLOHMANN_JSON_VERSION_MAJOR, NLOHMANN_JSON_VERSION_MINOR, NLOHMANN_JSON_VERSION_PATCH
```cpp
#define NLOHMANN_JSON_VERSION_MAJOR /* value */
#define NLOHMANN_JSON_VERSION_MINOR /* value */
#define NLOHMANN_JSON_VERSION_PATCH /* value */
```
These macros are defined by the library and contain the version numbers according to
[Semantic Versioning 2.0.0](https://semver.org/spec/v2.0.0.html).
## Default definition
The macros are defined according to the current library version.
## Examples
??? example
The example below shows how `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, and
`NLOHMANN_JSON_VERSION_PATCH` are defined by the library.
```cpp
--8<-- "examples/nlohmann_json_version.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_version.output"
```
## See also
- [meta](../basic_json/meta.md) - returns version information on the library
- [JSON_SKIP_LIBRARY_VERSION_CHECK](json_skip_library_version_check.md) - skip library version check
## Version history
- Added in version 3.1.0.
@@ -14,4 +14,4 @@
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>NLOHMANN_JSON_VERSION_PATCH</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>JSON</span><span class=w> </span><span class=kc>f</span><span class=err>or</span><span class=w> </span><span class=err>Moder</span><span class=kc>n</span><span class=w> </span><span class=err>C++</span><span class=w> </span><span class=err>versio</span><span class=kc>n</span><span class=w> </span><span class=mf>3.12.0</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/meta/ >meta</a> - returns version information on the library</li> <li><a href=../json_skip_library_version_check/ >JSON_SKIP_LIBRARY_VERSION_CHECK</a> - skip library version check</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../basic_json/meta/ >meta</a> - returns version information on the library</li> <li><a href=../json_skip_library_version_check/ >JSON_SKIP_LIBRARY_VERSION_CHECK</a> - skip library version check</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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@@ -0,0 +1,49 @@
# NLOHMANN_JSON_VERSION_MAJOR, NLOHMANN_JSON_VERSION_MINOR, NLOHMANN_JSON_VERSION_PATCH
```
#define NLOHMANN_JSON_VERSION_MAJOR /* value */
#define NLOHMANN_JSON_VERSION_MINOR /* value */
#define NLOHMANN_JSON_VERSION_PATCH /* value */
```
These macros are defined by the library and contain the version numbers according to [Semantic Versioning 2.0.0](https://semver.org/spec/v2.0.0.html).
## Default definition
The macros are defined according to the current library version.
## Examples
Example
The example below shows how `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, and `NLOHMANN_JSON_VERSION_PATCH` are defined by the library.
```
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
std::cout << "JSON for Modern C++ version "
<< NLOHMANN_JSON_VERSION_MAJOR << "."
<< NLOHMANN_JSON_VERSION_MINOR << "."
<< NLOHMANN_JSON_VERSION_PATCH << std::endl;
}
```
Output:
```
JSON for Modern C++ version 3.12.0
```
## See also
- [meta](https://json.nlohmann.me/api/basic_json/meta/index.md) - returns version information on the library
- [JSON_SKIP_LIBRARY_VERSION_CHECK](https://json.nlohmann.me/api/macros/json_skip_library_version_check/index.md) - skip library version check
## Version history
- Added in version 3.1.0.