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Author SHA1 Message Date
Niels Lohmann 45eac1eaa8 🧛 fix build
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-07-09 09:31:39 +02:00
Niels Lohmann cae5f17f83 📡 Document compiler/stdlib exclusions in macro_scope.hpp
Add "Known compiler/stdlib exclusions" subsections to the public documentation for
JSON_HAS_FILESYSTEM and JSON_HAS_RANGES, listing the exact compiler/stdlib versions
that are silently excluded even when feature-test macros indicate support. Each
exclusion references the originating issue. Also add a pointer note in the compiler
compatibility section linking to these details.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-Authored-By: Claude Code <noreply@anthropic.com>
2026-07-09 08:03:50 +02:00
30 changed files with 51 additions and 90 deletions
+1 -1
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@@ -109,7 +109,7 @@ A UTF-8 byte order mark is silently ignored.
- Added in version 3.0.0.
- Ignoring comments via `ignore_comments` added in version 3.9.0.
- Changed [runtime assertion](../../features/assertions.md) in case of `FILE*` null pointers to exception in version 3.12.0.
- Added `ignore_trailing_commas` in version 3.13.0.
- Added `ignore_trailing_commas` in version 3.12.x.
!!! warning "Deprecation"
+1 -1
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@@ -92,4 +92,4 @@ std::string format_as(const BasicJsonType& j)
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
-7
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@@ -114,13 +114,6 @@ overload (3).
See [Number conversion](../../features/types/number_handling.md#number-conversion)
for more information.
!!! note "`std::optional` conversions"
Prior to version 3.13.0, `#!cpp get<std::optional<T>>()` (and other conversions to `std::optional<T>`) failed to
compile in every configuration, due to an internal implementation bug that made the `from_json` overload for
`std::optional` unreachable regardless of the [`JSON_USE_IMPLICIT_CONVERSIONS`](../macros/json_use_implicit_conversions.md)
setting. This has been fixed.
## Examples
??? example
@@ -251,6 +251,5 @@ Strong exception safety: if an exception occurs, the original value stays intact
1. Added in version 1.0.0.
2. Added in version 1.0.0. Added overloads for `T* key` in version 1.1.0. Removed overloads for `T* key` (replaced by 3)
in version 3.11.0.
3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
already supported by [`at`](at.md), [`value`](value.md), [`find`](find.md), and other lookup functions.
3. Added in version 3.11.0.
4. Added in version 2.0.0.
+1 -1
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@@ -235,7 +235,7 @@ Invalid Unicode escapes and unpaired surrogates in the input are reported as
- Overload for contiguous containers (1) added in version 2.0.3.
- Ignoring comments via `ignore_comments` added in version 3.9.0.
- Changed [runtime assertion](../../features/assertions.md) in case of `FILE*` null pointers to exception in version 3.12.0.
- Added `ignore_trailing_commas` in version 3.13.0.
- Added `ignore_trailing_commas` in version 3.12.x.
!!! warning "Deprecation"
+1 -1
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@@ -74,4 +74,4 @@ is thrown. In any case, the original value is not changed: the patch is applied
- Added in version 2.0.0.
- Added [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) and stopped relying on an internal assertion when an "add" operation's
target location has a non-object/non-array parent in version 3.13.0.
target location has a non-object/non-array parent in version 3.12.x.
@@ -71,4 +71,4 @@ function throws an exception.
- Added in version 3.11.0.
- Added [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) and stopped relying on an internal assertion when an "add" operation's
target location has a non-object/non-array parent in version 3.13.0.
target location has a non-object/non-array parent in version 3.12.x.
+1 -1
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@@ -126,7 +126,7 @@ A UTF-8 byte order mark is silently ignored.
- Added in version 3.2.0.
- Ignoring comments via `ignore_comments` added in version 3.9.0.
- Added `ignore_trailing_commas` in version 3.13.0.
- Added `ignore_trailing_commas` in version 3.12.x.
!!! warning "Deprecation"
@@ -54,4 +54,4 @@ provides `<format>`, controlled by the [`JSON_HAS_STD_FORMAT`](../macros/json_ha
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
@@ -21,12 +21,6 @@ a string representation of the type ([`value_t`](value_t.md)):
| array | `"array"` |
| binary | `"binary"` |
| discarded | `"discarded"` |
| invalid (corrupted value) | `"invalid"` |
!!! note "The \"invalid\" type"
The `"invalid"` return value indicates a corrupted JSON value — this can occur if an enum value falls outside the
range of valid `value_t` values. This is useful for diagnosing data corruption or internal errors.
## Exception safety
@@ -58,4 +52,3 @@ Constant.
- Part of the public API version since 2.1.0.
- Changed return value to `const char*` and added `noexcept` in version 3.0.0.
- Added support for binary type in version 3.8.0.
- Added `"invalid"` return value for corrupted JSON values in version 3.13.0.
+1 -3
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@@ -184,6 +184,4 @@ changes to any JSON value.
1. Added in version 1.0.0. Changed parameter `default_value` type from `const ValueType&` to `ValueType&&` in version 3.11.0.
2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2.
3. Added in version 2.0.2. Extended to work with arrays in version 3.13.0, including fixing an issue where resolving
`ptr` through an array unexpectedly threw `out_of_range` instead of returning the resolved element (or
`default_value`, as documented).
3. Added in version 2.0.2. Extended to work with arrays in version 3.12.x.
+1 -1
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@@ -36,4 +36,4 @@ Constant.
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
@@ -32,4 +32,4 @@ Linear in the number of reference tokens in the `json_pointer`.
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
@@ -35,4 +35,4 @@ Linear in the number of reference tokens in the `json_pointer`.
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
@@ -92,4 +92,4 @@ The default value is `0` (disabled — existing behavior is preserved).
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
@@ -44,4 +44,4 @@ The default value is detected based on preprocessor macros such as `#!cpp __cplu
- Added in version 3.10.5.
- Added `JSON_HAS_CPP_23` in version 3.12.0.
- Added `JSON_HAS_CPP_26` in version 3.13.0.
- Added `JSON_HAS_CPP_26` in version 3.12.x.
@@ -19,6 +19,20 @@ The default value is detected based on the preprocessor macros `#!cpp __cpp_lib_
`#!cpp __cpp_lib_experimental_filesystem`, `#!cpp __has_include(<filesystem>)`, or
`#!cpp __has_include(<experimental/filesystem>)`.
!!! info "Known compiler/stdlib exclusions"
Even when the feature-test macro indicates filesystem support is available, the library disables it on the following broken toolchains:
- **MinGW + GCC 8** — disabled entirely (broken `std::filesystem` implementation; [MinGW-w64 bug 737](https://sourceforge.net/p/mingw-w64/bugs/737/))
- **GCC (non-Clang) < 8** — disabled (no filesystem support)
- **Clang < 7** — disabled (no filesystem support)
- **MSVC < 19.14** — disabled (no filesystem support)
- **iOS < 13** — disabled (no filesystem support)
- **macOS < Catalina (10.15)** — disabled (no filesystem support)
If `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` is `0` despite `__cpp_lib_filesystem` being defined, one
of the exclusions above likely applies to your toolchain.
## Notes
- Note that older compilers or older versions of libstdc++ also require the library `stdc++fs` to be linked to for
@@ -13,6 +13,18 @@ The default value is detected based on the preprocessor macro `#!cpp __cpp_lib_r
When the macro is not defined, the library will define it to its default value.
!!! info "Known compiler/stdlib exclusions"
Even when the feature-test macro `__cpp_lib_ranges` indicates ranges support is available, the library disables it on
the following incomplete or broken toolchains:
- **GCC 11.1.0** — disabled (the shipped `<ranges>` header has a syntax error; [issue #4440](https://github.com/nlohmann/json/issues/4440))
- **libstdc++ < 11** — disabled (incomplete C++20 ranges support; [issue #4440](https://github.com/nlohmann/json/issues/4440))
- **Clang < 16 with libstdc++** — disabled (incomplete ranges support; [issue #4440](https://github.com/nlohmann/json/issues/4440))
- **libc++ < 160000** — disabled (incomplete C++20 ranges support; [issue #4440](https://github.com/nlohmann/json/issues/4440))
If `JSON_HAS_RANGES` is `0` despite `__cpp_lib_ranges` being defined, one of the exclusions above likely applies to your toolchain.
## Examples
??? example
@@ -38,4 +38,4 @@ When the macro is not defined, the library will define it to its default value.
## Version history
- Added in version 3.13.0.
- Added in version 3.12.x.
@@ -75,4 +75,4 @@ For further information please refer to the corresponding macros without `WITH_N
## Version history
1. Added in version 3.13.0.
1. Added in version 3.12.x.
@@ -102,4 +102,4 @@ inline void from_json(const BasicJsonType& j, type& e);
## Version history
Added in version 3.13.0.
Added in version 3.12.x.
@@ -64,4 +64,4 @@ Linear.
- Added in version 1.0.0.
- Moved to namespace `nlohmann::literals::json_literals` in 3.11.0.
- Added `char8_t*` overload in 3.13.0.
- Added `char8_t*` overload in 3.12.x.
@@ -63,4 +63,4 @@ Linear.
- Added in version 2.0.0.
- Moved to namespace `nlohmann::literals::json_literals` in 3.11.0.
- Added `char8_t*` overload in 3.13.0.
- Added `char8_t*` overload in 3.12.x.
@@ -10,7 +10,7 @@ violations will result in a failed build.
Any compiler with complete C++11 support can compile the library without warnings.
Note: C++20 modules support may hit compiler-specific issues not covered by the general compiler matrix below. See [Modules](../features/modules.md#known-issues) for known issues and workarounds.
Note: Some modern features (like C++20 ranges or filesystem support) may be disabled on specific broken or incomplete toolchains even when standard feature-test macros indicate support. See [`JSON_HAS_RANGES`](../api/macros/json_has_ranges.md) and [`JSON_HAS_FILESYSTEM`](../api/macros/json_has_filesystem.md) for details on known exclusions.
- [x] The library is compiled with 50+ different C++ compilers with different operating systems and platforms,
including the oldest versions known to compile the library.
@@ -66,15 +66,7 @@ see "binary" cells in the table above.
!!! info "NaN/infinity handling"
`NaN`, `Infinity`, and `-Infinity` are serialized as a CBOR half-precision float (type 0xF9, 3 bytes total):
`NaN` as `0xF9 0x7E 0x00`, `Infinity` as `0xF9 0x7C 0x00`, and `-Infinity` as `0xF9 0xFC 0x00`. This behavior
differs from the normal JSON serialization which serializes NaN or Infinity to `null`.
!!! note
Prior to version 3.13.0, NaN and Infinity were instead serialized as a CBOR double-precision float (type 0xFB,
9 bytes total), because the check used to select a smaller encoding compared magnitudes with NaN, which is
always `false` and caused the intended half-precision path to be skipped.
If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the normal JSON serialization which serializes NaN or Infinity to `null`.
!!! info "Unused CBOR types"
@@ -168,13 +160,6 @@ The library maps CBOR types to JSON value types as follows:
- simple values (0xE0..0xF3, 0xF8)
- undefined (0xF7)
!!! warning "Negative integer overflow"
CBOR negative integers (major type 1) are decoded as `-1 - n`. If the encoded magnitude `n` is too large for the
result to fit into `number_integer_t` (`std::int64_t` by default), parsing fails with a
[`parse_error.112`](../../home/exceptions.md#jsonexceptionparse_error112) exception rather than overflowing
silently.
!!! warning "Object keys"
CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected.
@@ -67,15 +67,8 @@ specification:
!!! info "NaN/infinity handling"
`NaN`, `Infinity`, and `-Infinity` are serialized as a MessagePack float 32 (type 0xCA, 5 bytes total),
regardless of magnitude, in contrast to the [dump](../../api/basic_json/dump.md) function which serializes NaN
or Infinity to `null`.
!!! note
Prior to version 3.13.0, NaN and Infinity were instead serialized as a MessagePack float 64 (type 0xCB, 9 bytes
total), because the check used to select the smaller float 32 encoding compared magnitudes with NaN, which is
always `false` and caused the float 32 path to be skipped.
If NaN or Infinity are stored inside a JSON number, they are serialized properly in contrast to the
[dump](../../api/basic_json/dump.md) function which serializes NaN or Infinity to `null`.
??? example
-19
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@@ -27,7 +27,6 @@ json data = json::parse(f);
It should be noted that as modules do not export macros, the `nlohmann.json` module will not export any macros.
## Exported symbols
Only the following symbols are exported from `nlohmann.json`:
- `nlohmann::adl_serializer`
@@ -39,21 +38,3 @@ Only the following symbols are exported from `nlohmann.json`:
- `nlohmann::to_string`
- `nlohmann::literals::json_literals::operator""_json`
- `nlohmann::literals::json_literals::operator""_json_pointer`
Additionally, the following `nlohmann::detail` symbols are exported, solely to work around an MSVC compilation issue
([#3970](https://github.com/nlohmann/json/issues/3970)). They are implementation details, not part of the public API,
and should not be used directly:
- `nlohmann::detail::json_sax_dom_callback_parser`
- `nlohmann::detail::unknown_size`
## Known issues
C++20 modules support is exercised in CI against current GCC and Clang on Ubuntu, and the default MSVC toolset on Windows Server 2022 — there is no documented minimum compiler version, unlike feature-test-macro-gated features such as [`JSON_HAS_RANGES`](../api/macros/json_has_ranges.md).
!!! info "Known compiler issues"
- **GCC** may emit "redefinition" errors when `#include <nlohmann/json.hpp>` appears in a module preamble together with other imports. This is an upstream GCC bug, not yet resolved as of GCC 16. Workarounds: include `nlohmann/json.hpp` before other `#include`s, use `import nlohmann.json;` instead, or upgrade GCC. ([issue #5103](https://github.com/nlohmann/json/issues/5103))
- **MSVC** could fail with `C2039: 'json_sax_dom_callback_parser' is not a member of ... detail`; fixed by exporting the required internal symbols from `json.cppm` (see [Exported symbols](#exported-symbols) above). ([issue #3970](https://github.com/nlohmann/json/issues/3970))
If you hit a different module-related build failure, search [existing issues](https://github.com/nlohmann/json/issues?q=is%3Aissue+modules) before filing a new one.
@@ -63,10 +63,6 @@ In the default [`json`](../../api/json.md) type, numbers are stored as `#!c std:
number without loss of precision. If this is impossible (e.g., if the number is too large), the number is stored as
`#!c double`.
Positive integers are stored as `#!c std::uint64_t`, while negative integers are stored as `#!c std::int64_t`. This
distinction is determined at parse time: if the JSON number has a leading minus sign, it uses signed integer storage;
otherwise, it uses unsigned integer storage.
!!! info "Notes"
- Numbers with a decimal digit or scientific notation are always stored as `#!c double`.
+1 -4
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@@ -326,9 +326,6 @@ An unexpected byte was read in a [binary format](../features/binary_formats/inde
```
[json.exception.parse_error.112] parse error at byte 15: syntax error while parsing BSON binary: byte array length cannot be negative, is -1
```
```
[json.exception.parse_error.112] parse error at byte 9: syntax error while parsing CBOR value: negative integer overflow
```
### json.exception.parse_error.113
@@ -896,7 +893,7 @@ A JSON Patch `add` operation cannot be applied because the target location's par
!!! note
This exception was added in version 3.13.0. Before that, this situation hit an internal assertion (aborting the program in debug builds) or was silently ignored when assertions were disabled.
This exception was added in version 3.12.x. Before that, this situation hit an internal assertion (aborting the program in debug builds) or was silently ignored when assertions were disabled.
## Further exceptions
+1 -1
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@@ -178,7 +178,7 @@ See [this section](../features/types/number_handling.md#number-serialization) on
- Can I use `std::format("{}", j)` on a JSON value?
- Can I use `fmt::format("{}", j)` or `fmt::print("{}", j)` (the [{fmt}](https://github.com/fmtlib/fmt) library) on a JSON value?
`std::format` works out of the box since version 3.13.0, as long as the standard library provides
`std::format` works out of the box since version 3.12.x, as long as the standard library provides
`<format>` (see [`JSON_HAS_STD_FORMAT`](../api/macros/json_has_std_format.md)); see
[`std::formatter<basic_json>`](../api/basic_json/std_formatter.md) for details, including the `#!cpp "{:#}"`
pretty-print spec, indent widths (`#!cpp "{:2}"`), and custom indent characters (`#!cpp "{:.>#}"`).