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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 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_INTRUSIVE(type, member...)`

This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as serialization and (2) 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`, it can access private members. The first parameter is the name of the class/struct, and all remaining parameters name the members.

See full documentation of `NLOHMANN_DEFINE_TYPE_INTRUSIVE`.

## `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...)`

This macro is similar to `NLOHMANN_DEFINE_TYPE_INTRUSIVE`. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but can throw due to a mismatched type. The `from_json()` function default constructs an object and uses its values as the defaults when calling the `value` function.

See full documentation of `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT`.

## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...)`

This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object.

The macro is to be defined inside the namespace of the class/struct to create code for. Private members cannot be accessed. Use `NLOHMANN_DEFINE_TYPE_INTRUSIVE` in these scenarios. The first parameter is the name of the class/struct, and all remaining parameters name the members.

See full documentation of `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`.

## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...)`

This macro is similar to `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`. It will not throw an exception in `from_json()` due to a missing value in the JSON object, but can throw due to a mismatched type. The `from_json()` function default constructs an object and uses its values as the defaults when calling the `value` function.

See full documentation of `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`.

## `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.

See full documentation of `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, and `NLOHMANN_JSON_VERSION_PATCH`.

Last update: June 16, 2022
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