Macros¶

Some aspects of the library can be configured by defining preprocessor macros before including the json.hpp header. See also the macro overview page.

Runtime assertions¶

• JSON_ASSERT(x) - control behavior of runtime assertions

Exceptions¶

• JSON_CATCH_USER(exception)
  JSON_THROW_USER(exception)
  JSON_TRY_USER - control exceptions
• JSON_DIAGNOSTICS - control extended diagnostics
• JSON_NOEXCEPTION - switch off exceptions

Language support¶

• JSON_HAS_CPP_11
  JSON_HAS_CPP_14
  JSON_HAS_CPP_17
  JSON_HAS_CPP_20 - set supported C++ standard
• JSON_HAS_FILESYSTEM
  JSON_HAS_EXPERIMENTAL_FILESYSTEM - control std::filesystem support
• JSON_HAS_RANGES - control std::ranges support
• JSON_HAS_THREE_WAY_COMPARISON - control 3-way comparison support
• JSON_NO_IO - switch off functions relying on certain C++ I/O headers
• JSON_SKIP_UNSUPPORTED_COMPILER_CHECK - do not warn about unsupported compilers
• JSON_USE_GLOBAL_UDLS - place user-defined string literals (UDLs) into the global namespace

Library version¶

• JSON_SKIP_LIBRARY_VERSION_CHECK - skip library version check
• NLOHMANN_JSON_VERSION_MAJOR
  NLOHMANN_JSON_VERSION_MINOR
  NLOHMANN_JSON_VERSION_PATCH - library version information

Library namespace¶

• NLOHMANN_JSON_NAMESPACE - full name of the nlohmann namespace
• NLOHMANN_JSON_NAMESPACE_BEGIN
  NLOHMANN_JSON_NAMESPACE_END - open and close the library namespace
• NLOHMANN_JSON_NAMESPACE_NO_VERSION - disable the version component of the inline namespace

Type conversions¶

• JSON_DISABLE_ENUM_SERIALIZATION - switch off default serialization/deserialization functions for enums
• JSON_USE_IMPLICIT_CONVERSIONS - control implicit conversions

Comparison behavior¶

• JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON - control comparison of discarded values

Serialization/deserialization macros¶

• Enum: NLOHMANN_JSON_SERIALIZE_ENUM

• Class/struct:

  • Do you need to serialize private variables?
    • Yes? Do you only need serialization?
      • Yes? NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE
      • No? Allow deserialization of JSON values with missing values?
        • Yes? NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT
        • No? NLOHMANN_DEFINE_TYPE_INTRUSIVE
    • No? Do you only need serialization?
      • Yes? NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE
      • No? Allow deserialization of JSON values with missing values?
        • Yes? NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT
        • No? NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE

• NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...)
  NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(type, member...)
  NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(type, member...) - serialization/deserialization of types with access to private variables

• NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...)
  NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(type, member...)
  NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(type, member...) - serialization/deserialization of types without access to private variables
• NLOHMANN_JSON_SERIALIZE_ENUM(type, ...) - serialization/deserialization of enum types