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Niels Lohmann 6197341a21 Clean up non-code files (#5801) 
* Clean up README, contribution guide, and repository metadata

- REUSE.toml: fix the Hedley path and SPDX id (CC0-1.0), mark the docset
  icons as the public-domain JSON logo
- CITATION.cff: v3.12.0 was released on 2025-04-11
- FILES.md: list all workflows, describe the Meson option defaults
- README: ctest -LE, table of contents, typos, stale Android/MinGW advice,
  moved links, merge duplicate Thanks entries, list the analysis tools
  used in CI
- CONTRIBUTING: iterative parser, json_literals.hpp is generated, links
- .gitignore: backups and release outputs; .gitattributes: mark
  generated files
- labeler: label other build systems and .github documentation
- MODULE.bazel: add the module version

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Clean up CI, CMake, Makefile, and Bazel files

- CMakeLists.txt: avoid VERSION_GREATER_EQUAL, which CMake < 3.7 lacks
- ci.cmake: test JSON_DisableTupleReferenceConversion in ci_cmake_flags,
  remove unused variables and unreachable per-compiler targets, look up
  Clang tools consistently, forward CMAKE_CXX_FLAGS to ci_module_cpp20,
  format json_literals.hpp and remove backups in ci_test_amalgamation
- BUILD.bazel: add json_literals.hpp to the single-header target
- workflows: format json_literals.hpp before copying it, drop the obsolete
  natvis --version plumbing, name natvis and macro_builder in failure
  messages, drop the duplicate amalgamation job, install Valgrind only
  where needed, republish docs on version bumps, fix stale names
- Makefile: complete .PHONY and help, check-amalgamation always restores
  the checked-in files, natvis uses its own venv, macro_builder_check
  installs astyle, clean removes the fuzzer binaries
- remove tools/amalgamate/config_json_view.json (json_view.hpp is not on
  develop yet)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix inaccuracies in the documentation

- version history: json_base_class_t (3.11.3), JSON_HAS_CPP_11 (3.10.0),
  JSON_HAS_RANGES exclusions, define-type macros, ABI tags
- releases: 3.12.0 raised the minimum CMake version
- from_*: the (ptr, len) overloads are deleted, not removed, in 4.0.0
- contains/count/find: document the deleted integral overloads
- add JSON_HAS_RANGE_VIEW_CONVERSION and list the JSON_HAS_* macros in
  the macro overview
- mention BON8 and error_handler where binary formats are listed
- broken links, outdated URLs, warning count, Hunter v0.26.12
- copy_markdown_source hook: expand snippets in the Markdown copies

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Pass /EHsc to the Windows C++20 module build

ci_module_cpp20 now forwards CMAKE_CXX_FLAGS to the module build. The
Windows workflow sets CMAKE_CXX_FLAGS, which replaces CMake's MSVC
defaults including /EHsc, so <chrono> failed with C4530 under /WX.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-11 08:21:51 +02:00

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# Supported Macros
Some aspects of the library can be configured by defining preprocessor macros before including the `json.hpp` header.
See also the [API documentation for macros](../api/macros/index.md) for examples and more information.
## `JSON_ASSERT(x)`
This macro controls which code is executed for [runtime assertions](assertions.md) of the library.
See [full documentation of `JSON_ASSERT(x)`](../api/macros/json_assert.md).
## `JSON_BRACE_INIT_COPY_SEMANTICS`
When defined to `1`, single-element brace initialization of a `basic_json` value (e.g., `#!cpp json j{value};`) is
treated as a copy/move of the element rather than wrapping it in a single-element array. The default value is `0`, which
preserves the existing behavior.
See [full documentation of `JSON_BRACE_INIT_COPY_SEMANTICS`](../api/macros/json_brace_init_copy_semantics.md).
## `JSON_CATCH_USER(exception)`
This macro overrides [`#!cpp catch`](https://en.cppreference.com/w/cpp/language/try_catch) calls inside the library.
See [full documentation of `JSON_CATCH_USER(exception)`](../api/macros/json_throw_user.md).
## `JSON_DELETE_DEPRECATED_FUNCTIONS`
When defined to `1`, all deprecated functions are declared as deleted instead of only being marked as deprecated, so
code that still calls them no longer compiles. This way, you can find all calls that need to be replaced before version
4.0.0 removes these functions.
The macro can also be set with the CMake option
[`JSON_DeleteDeprecatedFunctions`](../integration/cmake.md#json_deletedeprecatedfunctions) (`OFF` by default).
See [full documentation of `JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md).
## `JSON_DIAGNOSTICS`
This macro enables extended diagnostics for exception messages. Possible values are `1` to enable or `0` to disable
(default).
When enabled, exception messages contain a [JSON Pointer](json_pointer.md) to the JSON value that triggered the
exception, see [Extended diagnostic messages](../home/exceptions.md#extended-diagnostic-messages) for an example. Note
that enabling this macro increases the size of every JSON value by one pointer and adds some runtime overhead.
The diagnostics messages can also be controlled with the CMake option
[`JSON_Diagnostics`](../integration/cmake.md#json_diagnostics) (`OFF` by default) which sets `JSON_DIAGNOSTICS`
accordingly.
See [full documentation of `JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md).
## `JSON_DIAGNOSTIC_POSITIONS`
When enabled, two new member functions [`start_pos()`](../api/basic_json/start_pos.md) and
[`end_pos()`](../api/basic_json/end_pos.md) are added to [`basic_json`](../api/basic_json/index.md) values. If the value
was created by calling the[`parse`](../api/basic_json/parse.md) function, then these functions allow querying the byte
positions of the value in the input it was parsed from. The byte positions are also used in exceptions to help locate
errors.
The diagnostics positions can also be controlled with the CMake option
[`JSON_Diagnostic_Positions`](../integration/cmake.md#json_diagnostic_positions) (`OFF` by default) which sets
`JSON_DIAGNOSTIC_POSITIONS` accordingly.
See [full documentation of `JSON_DIAGNOSTIC_POSITIONS`](../api/macros/json_diagnostic_positions.md)
## `JSON_HAS_CPP_11`, `JSON_HAS_CPP_14`, `JSON_HAS_CPP_17`, `JSON_HAS_CPP_20`, `JSON_HAS_CPP_23`, `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.
See [full documentation of `JSON_HAS_CPP_11`, `JSON_HAS_CPP_14`, `JSON_HAS_CPP_17`, `JSON_HAS_CPP_20`, `JSON_HAS_CPP_23`, and `JSON_HAS_CPP_26`](../api/macros/json_has_cpp_11.md).
## `JSON_HAS_FILESYSTEM`, `JSON_HAS_EXPERIMENTAL_FILESYSTEM`
When compiling with C++17, the library provides conversions from and to `std::filesystem::path`. As compiler support
for filesystem is limited, the library tries to detect whether `<filesystem>`/`std::filesystem` (`JSON_HAS_FILESYSTEM`)
or `<experimental/filesystem>`/`std::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`.
See [full documentation of `JSON_HAS_FILESYSTEM` and `JSON_HAS_EXPERIMENTAL_FILESYSTEM`](../api/macros/json_has_filesystem.md).
## `JSON_HAS_RANGES`
The library uses `std::ranges` (and concepts) where available, for example, to parse from C++20 ranges and to
construct JSON arrays from range views. The library detects whether the standard library supports ranges and
disables the support on toolchains with an incomplete implementation. To override the built-in check, define
`JSON_HAS_RANGES` to `1` or `0`.
See [full documentation of `JSON_HAS_RANGES`](../api/macros/json_has_ranges.md).
## `JSON_HAS_RANGE_VIEW_CONVERSION`
When `JSON_HAS_RANGES` is enabled (and the compiler is not MinGW), a JSON array can be constructed directly from a C++20
range view such as `std::views::filter(...)`. To override the built-in check, define `JSON_HAS_RANGE_VIEW_CONVERSION` to
`1` or `0`.
See [full documentation of `JSON_HAS_RANGE_VIEW_CONVERSION`](../api/macros/json_has_range_view_conversion.md).
## `JSON_HAS_STATIC_RTTI`
The library detects whether the compiler supports run time type information (RTTI), which it needs, for instance, to
exclude `std::any` from the candidate types of the implicit conversion on C++17. To override the built-in check, define
`JSON_HAS_STATIC_RTTI` to `1` or `0`.
See [full documentation of `JSON_HAS_STATIC_RTTI`](../api/macros/json_has_static_rtti.md).
## `JSON_HAS_STD_FORMAT`
When compiling with C++20 and a standard library that provides `<format>`, the library provides a `std::formatter`
specialization for JSON values. To override the built-in check, define `JSON_HAS_STD_FORMAT` to `1` or `0`.
See [full documentation of `JSON_HAS_STD_FORMAT`](../api/macros/json_has_std_format.md).
## `JSON_HAS_THREE_WAY_COMPARISON`
When the compiler and standard library support 3-way comparison (the spaceship operator `<=>`), the library provides it
for JSON values. To override the built-in check, define `JSON_HAS_THREE_WAY_COMPARISON` to `1` or `0`.
See [full documentation of `JSON_HAS_THREE_WAY_COMPARISON`](../api/macros/json_has_three_way_comparison.md).
## `JSON_NOEXCEPTION`
Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`.
See [full documentation of `JSON_NOEXCEPTION`](../api/macros/json_noexception.md).
## `JSON_DISABLE_ENUM_SERIALIZATION`
When defined, default parse and serialize functions for enums are excluded and have to be provided by the user, for example, using [`NLOHMANN_JSON_SERIALIZE_ENUM`](../api/macros/nlohmann_json_serialize_enum.md).
See [full documentation of `JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json_disable_enum_serialization.md).
## `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`
When defined to `1`, a JSON value can no longer be created from a one-element `std::tuple` holding a reference to a JSON
value, such as the result of `std::forward_as_tuple(j)`. This lets `std::tuple` convert such tuples element-wise. This
is planned to become the default in version 4.0.0.
See [full documentation of `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md).
## `JSON_NO_AUTOMATIC_UDLS`
When defined, `<nlohmann/json.hpp>` does not include `<nlohmann/json_literals.hpp>` with the user-defined string literals
`operator""_json` and `operator""_json_pointer`. This reduces the compile time of translation units that do not use
them, because the literals instantiate the parser in every translation unit that includes them. Include
`<nlohmann/json_literals.hpp>` where the literals are needed.
See [full documentation of `JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md).
## `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 environment where these I/O functions are disallowed for
security reasons (e.g., Intel Software Guard Extensions (SGX)).
See [full documentation of `JSON_NO_IO`](../api/macros/json_no_io.md).
## `JSON_NO_THREAD_LOCAL`
When defined, the library does not use `#!cpp thread_local` storage. Copying a value and comparing two values then
always avoid the call stack rather than descending into a bounded number of levels first, which is slower but yields the
same values and the same comparisons.
See [full documentation of `JSON_NO_THREAD_LOCAL`](../api/macros/json_no_thread_local.md).
## `JSON_PRECISE_STREAM_POSITION`
When defined to `1`, [`operator>>`](../api/operator_gtgt.md) and non-strict
[`sax_parse`](../api/basic_json/sax_parse.md) leave an input stream positioned right after the parsed value, instead of
also consuming the character that terminates a number. The default value is `0`, which preserves the existing behavior;
this is planned to become the default in version 4.0.0.
See [full documentation of `JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md).
## `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.
See [full documentation of `JSON_SKIP_LIBRARY_VERSION_CHECK`](../api/macros/json_skip_library_version_check.md).
## `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.
See [full documentation of `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`](../api/macros/json_skip_unsupported_compiler_check.md).
## `JSON_STRICT_BINARY_UTF8`
When defined to `1`, [`to_cbor`](../api/basic_json/to_cbor.md), [`to_ubjson`](../api/basic_json/to_ubjson.md),
[`to_bjdata`](../api/basic_json/to_bjdata.md), and [`to_bson`](../api/basic_json/to_bson.md) throw
[`type_error.316`](../home/exceptions.md#jsonexceptiontype_error316) for a string value or object key that is not
valid UTF-8. The default value is `0`, which writes the bytes unchanged as before version 3.13.0; this is planned to
become the default in version 4.0.0.
The check can also be enabled with the CMake option
[`JSON_StrictBinaryUTF8`](../integration/cmake.md#json_strictbinaryutf8) (`OFF` by default) which sets
`JSON_STRICT_BINARY_UTF8` accordingly.
See [full documentation of `JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md).
## `JSON_STRICT_NUL_HANDLING`
When defined to `1`, a `'\0'` (NUL) byte anywhere in the input is rejected with `parse_error.101`, like any other
unexpected byte, instead of being silently treated as end of input (see the
[FAQ entry](../home/faq.md#nul-bytes-in-the-input) for background). The default value is `0`, which preserves the
existing behavior; this is planned to become the default in version 4.0.0.
The strict handling can also be enabled with the CMake option
[`JSON_StrictNulHandling`](../integration/cmake.md#json_strictnulhandling) (`OFF` by default) which sets
`JSON_STRICT_NUL_HANDLING` accordingly.
See [full documentation of `JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md).
## `JSON_THROW_USER(exception)`
This macro overrides `#!cpp throw` calls inside the library. The argument is the exception to be thrown.
See [full documentation of `JSON_THROW_USER(exception)`](../api/macros/json_throw_user.md).
## `JSON_TRY_USER`
This macro overrides `#!cpp try` calls inside the library.
See [full documentation of `JSON_TRY_USER`](../api/macros/json_throw_user.md).
## `JSON_USE_IMPLICIT_CONVERSIONS`
When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on.
See [full documentation of `JSON_USE_IMPLICIT_CONVERSIONS`](../api/macros/json_use_implicit_conversions.md).
## `JSON_USE_GLOBAL_UDLS`
When defined to `1` (default), the user-defined string literals `operator""_json` and `operator""_json_pointer` are
placed into the global namespace instead of `nlohmann::literals::json_literals`.
See [full documentation of `JSON_USE_GLOBAL_UDLS`](../api/macros/json_use_global_udls.md).
## `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`
When defined to `1`, the library restores the legacy behavior in which a discarded value compared equal to itself. This
behavior is [deprecated](../integration/migration_guide.md#miscellaneous-functions) and switched off (`0`) by
default.
See [full documentation of `JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](../api/macros/json_use_legacy_discarded_value_comparison.md).
## `JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`
When defined to `1`, maps with enum keys (e.g., `std::map<E, T>`) are stored as objects, using the enum's conversion for
the keys, instead of arrays of `[key, value]` pairs. It is switched off (`0`) by default.
See [full documentation of `JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md).
## `JSON_USE_SIMDUTF`
When defined, UTF-8 validation of JSON strings read from contiguous byte input is delegated to the
[simdutf](https://github.com/simdutf/simdutf) library instead of the built-in scalar validator. This is an opt-in
external dependency and is not defined by default.
See [full documentation of `JSON_USE_SIMDUTF`](../api/macros/json_use_simdutf.md).
## `NLOHMANN_DEFINE_TYPE_*(...)`, `NLOHMANN_DEFINE_DERIVED_TYPE_*(...)`
The library defines 12 macros to simplify the serialization/deserialization of types. See the page on
[arbitrary type conversion](arbitrary_types.md#simplify-your-life-with-macros) for a detailed discussion.
## `NLOHMANN_JSON_NAMESPACE`, `NLOHMANN_JSON_NAMESPACE_BEGIN`, `NLOHMANN_JSON_NAMESPACE_END`, `NLOHMANN_JSON_NAMESPACE_NO_VERSION`
These macros relate to the versioned, inline `nlohmann` namespace:
- `NLOHMANN_JSON_NAMESPACE` evaluates to the full name of the `nlohmann` namespace (including the inline ABI namespace).
- `NLOHMANN_JSON_NAMESPACE_BEGIN` / `NLOHMANN_JSON_NAMESPACE_END` open and close the namespace (for example, to add
specializations).
- `NLOHMANN_JSON_NAMESPACE_NO_VERSION`, when defined to `1`, omits the version component from the inline namespace.
See the [`nlohmann` Namespace](namespace.md) page, and the full documentation of
[`NLOHMANN_JSON_NAMESPACE`](../api/macros/nlohmann_json_namespace.md),
[`NLOHMANN_JSON_NAMESPACE_BEGIN` / `NLOHMANN_JSON_NAMESPACE_END`](../api/macros/nlohmann_json_namespace_begin.md), and
[`NLOHMANN_JSON_NAMESPACE_NO_VERSION`](../api/macros/nlohmann_json_namespace_no_version.md).
## `NLOHMANN_JSON_SERIALIZE_ENUM(type, ...)`
This macro simplifies the serialization/deserialization of enum types. See
[Specializing enum conversion](enum_conversion.md) for more information.
See [full documentation of `NLOHMANN_JSON_SERIALIZE_ENUM`](../api/macros/nlohmann_json_serialize_enum.md).
A strict variant [`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../api/macros/nlohmann_json_serialize_enum_strict.md) throws an
exception on undefined input instead of falling back to the first mapping.
## `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, `NLOHMANN_JSON_VERSION_PATCH`
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).
See [full documentation of `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, and `NLOHMANN_JSON_VERSION_PATCH`](../api/macros/nlohmann_json_version_major.md).
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