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148 lines
7.7 KiB
Markdown
148 lines
7.7 KiB
Markdown
# Supported Macros
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Some aspects of the library can be configured by defining preprocessor macros before including the `json.hpp` header.
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See also the [API documentation for macros](../api/macros/index.md) for examples and more information.
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## `JSON_ASSERT(x)`
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This macro controls which code is executed for [runtime assertions](assertions.md) of the library.
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See [full documentation of `JSON_ASSERT(x)`](../api/macros/json_assert.md).
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## `JSON_CATCH_USER(exception)`
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This macro overrides [`#!cpp catch`](https://en.cppreference.com/w/cpp/language/try_catch) calls inside the library.
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See [full documentation of `JSON_CATCH_USER(exception)`](../api/macros/json_throw_user.md).
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## `JSON_DIAGNOSTICS`
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This macro enables extended diagnostics for exception messages. Possible values are `1` to enable or `0` to disable
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(default).
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When enabled, exception messages contain a [JSON Pointer](json_pointer.md) to the JSON value that triggered the
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exception, see [Extended diagnostic messages](../home/exceptions.md#extended-diagnostic-messages) for an example. Note
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that enabling this macro increases the size of every JSON value by one pointer and adds some runtime overhead.
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The diagnostics messages can also be controlled with the CMake option `JSON_Diagnostics` (`OFF` by default) which sets
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`JSON_DIAGNOSTICS` accordingly.
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See [full documentation of `JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md).
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## `JSON_HAS_CPP_11`, `JSON_HAS_CPP_14`, `JSON_HAS_CPP_17`, `JSON_HAS_CPP_20`
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The library targets C++11, but also supports some features introduced in later C++ versions (e.g., `std::string_view`
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support for C++17). For these new features, the library implements some preprocessor checks to determine the C++
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standard. By defining any of these symbols, the internal check is overridden and the provided C++ version is
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unconditionally assumed. This can be helpful for compilers that only implement parts of the standard and would be
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detected incorrectly.
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See [full documentation of `JSON_HAS_CPP_11`, `JSON_HAS_CPP_14`, `JSON_HAS_CPP_17`, and `JSON_HAS_CPP_20`](../api/macros/json_has_cpp_11.md).
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## `JSON_HAS_FILESYSTEM`, `JSON_HAS_EXPERIMENTAL_FILESYSTEM`
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When compiling with C++17, the library provides conversions from and to `std::filesystem::path`. As compiler support
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for filesystem is limited, the library tries to detect whether `<filesystem>`/`std::filesystem` (`JSON_HAS_FILESYSTEM`)
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or `<experimental/filesystem>`/`std::experimental::filesystem` (`JSON_HAS_EXPERIMENTAL_FILESYSTEM`) should be used.
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To override the built-in check, define `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` to `1`.
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See [full documentation of `JSON_HAS_FILESYSTEM` and `JSON_HAS_EXPERIMENTAL_FILESYSTEM`](../api/macros/json_has_filesystem.md).
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## `JSON_NOEXCEPTION`
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Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`.
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See [full documentation of `JSON_NOEXCEPTION`](../api/macros/json_noexception.md).
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## `JSON_NO_IO`
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When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>` are not included and parse functions
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relying on these headers are excluded. This is relevant for environment where these I/O functions are disallowed for
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security reasons (e.g., Intel Software Guard Extensions (SGX)).
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See [full documentation of `JSON_NO_IO`](../api/macros/json_no_io.md).
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## `JSON_SKIP_LIBRARY_VERSION_CHECK`
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When defined, the library will not create a compiler warning when a different version of the library was already
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included.
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See [full documentation of `JSON_SKIP_LIBRARY_VERSION_CHECK`](../api/macros/json_skip_library_version_check.md).
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## `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`
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When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows to
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use the library with compilers that do not fully support C++11 and may only work if unsupported features are not used.
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See [full documentation of `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`](../api/macros/json_skip_unsupported_compiler_check.md).
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## `JSON_THROW_USER(exception)`
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This macro overrides `#!cpp throw` calls inside the library. The argument is the exception to be thrown.
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See [full documentation of `JSON_THROW_USER(exception)`](../api/macros/json_throw_user.md).
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## `JSON_TRY_USER`
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This macro overrides `#!cpp try` calls inside the library.
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See [full documentation of `JSON_TRY_USER`](../api/macros/json_throw_user.md).
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## `JSON_USE_IMPLICIT_CONVERSIONS`
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When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on.
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See [full documentation of `JSON_USE_IMPLICIT_CONVERSIONS`](../api/macros/json_use_implicit_conversions.md).
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## `NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...)`
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This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as
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serialization and (2) want to use the member variable names as object keys in that object.
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The macro is to be defined inside the class/struct to create code for. Unlike
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[`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](#nlohmann_define_type_non_intrusivetype-member), it can access private members.
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The first parameter is the name of the class/struct, and all remaining parameters name the members.
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See [full documentation of `NLOHMANN_DEFINE_TYPE_INTRUSIVE`](../api/macros/nlohmann_define_type_intrusive.md).
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## `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...)`
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This macro is similar to `NLOHMANN_DEFINE_TYPE_INTRUSIVE`. It will not throw an exception in `from_json()` due to a
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missing value in the JSON object, but can throw due to a mismatched type. The `from_json()` function default constructs
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an object and uses its values as the defaults when calling the [`value`](../api/basic_json/value.md) function.
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See [full documentation of `NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT`](../api/macros/nlohmann_define_type_intrusive.md).
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## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...)`
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This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as
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serialization and (2) want to use the member variable names as object keys in that object.
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The macro is to be defined inside the namespace of the class/struct to create code for. Private members cannot be
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accessed. Use [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](#nlohmann_define_type_intrusivetype-member) in these scenarios. The
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first parameter is the name of the class/struct, and all remaining parameters name the members.
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See [full documentation of `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](../api/macros/nlohmann_define_type_non_intrusive.md).
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## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...)`
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This macro is similar to `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`. It will not throw an exception in `from_json()` due to a
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missing value in the JSON object, but can throw due to a mismatched type. The `from_json()` function default constructs
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an object and uses its values as the defaults when calling the [`value`](../api/basic_json/value.md) function.
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See [full documentation of `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT`](../api/macros/nlohmann_define_type_non_intrusive.md).
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## `NLOHMANN_JSON_SERIALIZE_ENUM(type, ...)`
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This macro simplifies the serialization/deserialization of enum types. See
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[Specializing enum conversion](enum_conversion.md) for more information.
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See [full documentation of `NLOHMANN_JSON_SERIALIZE_ENUM`](../api/macros/nlohmann_json_serialize_enum.md).
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## `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, `NLOHMANN_JSON_VERSION_PATCH`
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These macros are defined by the library and contain the version numbers according to
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[Semantic Versioning 2.0.0](https://semver.org/spec/v2.0.0.html).
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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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