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 for examples and more information.
JSON_ASSERT(x)¶
This macro controls which code is executed for runtime assertions of the library.
See full documentation of JSON_ASSERT(x).
JSON_CATCH_USER(exception)¶
This macro overrides catch calls inside the library.
See full documentation of JSON_CATCH_USER(exception).
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 to the JSON value that triggered the exception, see 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 (OFF by default) which sets JSON_DIAGNOSTICS accordingly.
See full documentation of JSON_DIAGNOSTICS.
JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20¶
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, and JSON_HAS_CPP_20.
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.
JSON_NOEXCEPTION¶
Exceptions can be switched off by defining the symbol JSON_NOEXCEPTION.
See full documentation of JSON_NOEXCEPTION.
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.
See full documentation of JSON_DISABLE_ENUM_SERIALIZATION.
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.
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.
JSON_SKIP_UNSUPPORTED_COMPILER_CHECK¶
When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows to use 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.
JSON_THROW_USER(exception)¶
This macro overrides throw calls inside the library. The argument is the exception to be thrown.
See full documentation of JSON_THROW_USER(exception).
JSON_TRY_USER¶
This macro overrides try calls inside the library.
See full documentation of JSON_TRY_USER.
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.
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 for a detailed discussion.
NLOHMANN_JSON_SERIALIZE_ENUM(type, ...)¶
This macro simplifies the serialization/deserialization of enum types. See Specializing enum conversion for more information.
See full documentation of NLOHMANN_JSON_SERIALIZE_ENUM.
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.