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Niels Lohmann 6fc0d501f3 Move the user-defined string literals to <nlohmann/json_literals.hpp> and add JSON_NO_AUTOMATIC_UDLS (#5610 )

* Add JSON_NO_UDLS to leave out the user-defined string literals

The bodies of operator""_json and operator""_json_pointer call the
parser, so every translation unit including the library instantiates it,
even if it never parses anything. Defining JSON_NO_UDLS leaves the
literals out entirely, which saves 15-35% compile time for such
translation units (#5294). Nothing changes if the macro is not defined.

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

* Mention JSON_NO_UDLS in the list of exported module symbols

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

* Move the user-defined string literals to <nlohmann/json_literals.hpp>

Following the review in #5294, the literals now live in their own header
instead of being removed entirely: <nlohmann/json.hpp> includes it at the
end unless JSON_NO_AUTOMATIC_UDLS (renamed from JSON_NO_UDLS) is defined,
so a project can opt out globally and include the header only where the
literals are used.

The header only uses public and standard macros, because the library's
internal macros are undefined at the end of json.hpp and the amalgamation
inlines macro_scope.hpp only once. For the same reason, the library no
longer defines and undefines JSON_USE_GLOBAL_UDLS, so a user's definition
is still visible to the header. The single-header copy is identical to
the multi-header one, as it only includes <nlohmann/json.hpp>. The module
always exports the literals.

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

* Fix CI: include cycle, GCC 4.8 literal operator spacing, and global UDLs off in the JSON_NO_AUTOMATIC_UDLS test

- Suppress clang-tidy misc-header-include-cycle on the intentional mutual
  include of json.hpp and json_literals.hpp.
- Use operator"" _json with a space for GCC 4.8 in the test's detection
  aliases, as the header does.
- Only test the global literal operators when JSON_USE_GLOBAL_UDLS is on.

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

* Declare the literal operators through a local macro

The GCC 4.8 spacing condition was repeated for both operator definitions
and the global using-declarations. NLOHMANN_JSON_LITERAL_OPERATOR(suffix)
now selects operator""##suffix or operator"" suffix in one place and is
undefined at the end of json_literals.hpp.

Suggested by gregmarr in review.

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

---------

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

2026-09-30 20:08:17 +02:00

7.6 KiB

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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_DIAGNOSTIC_POSITIONS - access positions of elements
JSON_NOEXCEPTION - switch off exceptions

Parsing

JSON_PRECISE_STREAM_POSITION - opt in to leaving an input stream positioned right after a parsed number
JSON_STRICT_NUL_HANDLING - opt in to rejecting a NUL byte in the input instead of treating it as end of input

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_STD_FORMAT - control std::format/std::formatter support
JSON_HAS_THREE_WAY_COMPARISON - control 3-way comparison support
JSON_NO_AUTOMATIC_UDLS - do not include the user-defined string literals (UDLs) automatically
JSON_NO_IO - switch off functions relying on certain C++ I/O headers
JSON_NO_THREAD_LOCAL - switch off the use of thread_local storage
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
JSON_USE_SIMDUTF - use the simdutf library to accelerate UTF-8 validation

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_BRACE_INIT_COPY_SEMANTICS - opt in to copy/move semantics for single-element brace initialization
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

Enums

NLOHMANN_JSON_SERIALIZE_ENUM - serialize/deserialize an enum
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT - serialize/deserialize an enum with exceptions

Classes and structs

NLOHMANN_DEFINE_TYPE_INTRUSIVE - serialize/deserialize a non-derived class with private members
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a non-derived class with private members; uses default values
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE - serialize a non-derived class with private members
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE - serialize/deserialize a non-derived class
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a non-derived class; uses default values
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - serialize a non-derived class
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE - serialize/deserialize a derived class with private members
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a derived class with private members; uses default values
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE - serialize a derived class with private members
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE - serialize/deserialize a derived class
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a derived class; uses default values
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - serialize a derived class
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES - serialize/deserialize a non-derived class with private members; uses custom names
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a non-derived class with private members; uses default values; uses custom names
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a non-derived class with private members; uses custom names
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES - serialize/deserialize a non-derived class; uses custom names
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a non-derived class; uses default values; uses custom names
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a non-derived class; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES - serialize/deserialize a derived class with private members; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a derived class with private members; uses default values; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a derived class with private members; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES - serialize/deserialize a derived class; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a derived class; uses default values; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a derived class; uses custom names

7.6 KiB Raw Blame History