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json/docs/mkdocs/docs/api/macros/index.md
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Niels Lohmann c6742f9761 Scan strings with SSE2, SSSE3, or NEON 
The string fast path found the end of a run of plain characters 8 bytes at
a time (SWAR) and validated non-ASCII text one sequence at a time, calling
validate_one_utf8() out of line for each.

The vector code of json_view's scanner, in the new shared header
detail/input/simd_scan.hpp, now does both 16 bytes at a time: SSE2 finds
the end of a run on x86-64, and the UTF-8 check of Keiser and Lemire runs
with NEON on AArch64 and with SSSE3 on x86-64. SSSE3 is not part of x86-64,
so the check is compiled for it with a function attribute and used when the
CPU has it (cached in a constant-initialized atomic), else the scalar check;
code compiled with -mssse3 skips the CPU check. The first word of a run is
still checked with SWAR (the first four with NEON, where a vector mask
costs more), as most keys and short values end there, and the scalar
helpers are always inlined. On anything else, the scalar code is unchanged.

The new macro JSON_NO_SIMD selects the portable code everywhere, including
the SSE2/NEON digit formatting of the floating-point writer. The lexer tests
now also run with JSON_NO_SIMD and, on x86-64, with -mssse3, and a new test
places every byte that ends a run at each offset across several 16-byte
blocks, after ASCII and after CJK text.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-15 18:37:04 +02:00

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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](../../features/macros.md).
## Runtime assertions
- [**JSON_ASSERT(x)**](json_assert.md) - control behavior of runtime assertions
## Exceptions
- [**JSON_CATCH_USER(exception)**<br>**JSON_THROW_USER(exception)**<br>**JSON_TRY_USER**](json_throw_user.md) - control exceptions
- [**JSON_DIAGNOSTICS**](json_diagnostics.md) - control extended diagnostics
- [**JSON_DIAGNOSTIC_POSITIONS**](json_diagnostic_positions.md) - access positions of elements
- [**JSON_NOEXCEPTION**](json_noexception.md) - switch off exceptions
## Parsing
- [**JSON_DISABLE_STREAM_BULK_SCAN**](json_disable_stream_bulk_scan.md) - read a `std::istream` one character at a time
instead of scanning its stream buffer in bulk
- [**JSON_DISABLE_UNLOCKED_FILE_IO**](json_disable_unlocked_file_io.md) - read a `FILE*` with `std::fgetc` instead of
locking it once and using the unlocked stdio functions
- [**JSON_PRECISE_STREAM_POSITION**](json_precise_stream_position.md) - opt in to leaving an input stream positioned
right after a parsed number
- [**JSON_STRICT_BINARY_UTF8**](json_strict_binary_utf8.md) - opt in to checking strings for valid UTF-8 in the CBOR,
UBJSON, BJData, and BSON writers
- [**JSON_STRICT_NUL_HANDLING**](json_strict_nul_handling.md) - opt in to rejecting a NUL byte in the input instead of
treating it as end of input
## Language support
- [**JSON_HAS_CPP_11**<br>**JSON_HAS_CPP_14**<br>**JSON_HAS_CPP_17**<br>**JSON_HAS_CPP_20**](json_has_cpp_11.md) - set supported C++ standard
- [**JSON_HAS_FILESYSTEM**<br>**JSON_HAS_EXPERIMENTAL_FILESYSTEM**](json_has_filesystem.md) - control `std::filesystem` support
- [**JSON_HAS_RANGE_VIEW_CONVERSION**](json_has_range_view_conversion.md) - control construction from `std::ranges` views
- [**JSON_HAS_RANGES**](json_has_ranges.md) - control `std::ranges` support
- [**JSON_HAS_STATIC_RTTI**](json_has_static_rtti.md) - control RTTI (run time type information) support
- [**JSON_HAS_STD_FORMAT**](json_has_std_format.md) - control `std::format`/`std::formatter` support
- [**JSON_HAS_THREE_WAY_COMPARISON**](json_has_three_way_comparison.md) - control 3-way comparison support
- [**JSON_NO_AUTOMATIC_UDLS**](json_no_automatic_udls.md) - do not include the user-defined string literals (UDLs) automatically
- [**JSON_NO_IO**](json_no_io.md) - switch off functions relying on certain C++ I/O headers
- [**JSON_NO_SIMD**](json_no_simd.md) - use only portable code instead of vector instructions (SSE2, SSSE3, NEON)
- [**JSON_NO_THREAD_LOCAL**](json_no_thread_local.md) - switch off the use of `thread_local` storage
- [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](json_skip_unsupported_compiler_check.md) - do not warn about unsupported compilers
- [**JSON_USE_GLOBAL_UDLS**](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
- [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
## Library version
- [**JSON_SKIP_LIBRARY_VERSION_CHECK**](json_skip_library_version_check.md) - skip library version check
- [**NLOHMANN_JSON_VERSION_MAJOR**<br>**NLOHMANN_JSON_VERSION_MINOR**<br>**NLOHMANN_JSON_VERSION_PATCH**](nlohmann_json_version_major.md)
\- library version information
## Library namespace
- [**NLOHMANN_JSON_NAMESPACE**](nlohmann_json_namespace.md) - full name of the `nlohmann` namespace
- [**NLOHMANN_JSON_NAMESPACE_BEGIN**<br>**NLOHMANN_JSON_NAMESPACE_END**](nlohmann_json_namespace_begin.md) - open and
close the library namespace
- [**NLOHMANN_JSON_NAMESPACE_NO_VERSION**](nlohmann_json_namespace_no_version.md) - disable the version component of
the inline namespace
## Type conversions
- [**JSON_BRACE_INIT_COPY_SEMANTICS**](json_brace_init_copy_semantics.md) - opt in to copy/move semantics for single-element brace initialization
- [**JSON_DISABLE_ENUM_SERIALIZATION**](json_disable_enum_serialization.md) - switch off default serialization/deserialization functions for enums
- [**JSON_DISABLE_TUPLE_REFERENCE_CONVERSION**](json_disable_tuple_reference_conversion.md) - switch off conversion from a one-element tuple of a JSON reference
- [**JSON_USE_IMPLICIT_CONVERSIONS**](json_use_implicit_conversions.md) - control implicit conversions
- [**JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS**](json_use_objects_for_enum_keyed_maps.md) - opt in to storing maps with enum
keys as objects
## Deprecated functions
- [**JSON_DELETE_DEPRECATED_FUNCTIONS**](json_delete_deprecated_functions.md) - opt in to deleting the deprecated
functions ahead of their removal in version 4.0.0
## Comparison behavior
- [**JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON**](json_use_legacy_discarded_value_comparison.md) -
control comparison of discarded values
## Serialization/deserialization macros
### Enums
- [**NLOHMANN_JSON_SERIALIZE_ENUM**](nlohmann_json_serialize_enum.md) - serialize/deserialize an enum
- [**NLOHMANN_JSON_SERIALIZE_ENUM_STRICT**](nlohmann_json_serialize_enum_strict.md) - serialize/deserialize an enum with exceptions
### Classes and structs
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE**](nlohmann_define_type_intrusive.md) - serialize/deserialize a non-derived class
with private members
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT**](nlohmann_define_type_intrusive.md) - serialize/deserialize a
non-derived class with private members; uses default values
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE**](nlohmann_define_type_intrusive.md) - serialize a non-derived class
with private members
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE**](nlohmann_define_type_non_intrusive.md) - serialize/deserialize a non-derived
class
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT**](nlohmann_define_type_non_intrusive.md) - serialize/deserialize a
non-derived class; uses default values
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE**](nlohmann_define_type_non_intrusive.md) - serialize a
non-derived class
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE**](nlohmann_define_derived_type.md) - serialize/deserialize a derived class
with private members
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT**](nlohmann_define_derived_type.md) - serialize/deserialize a
derived class with private members; uses default values
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE**](nlohmann_define_derived_type.md) - serialize a derived
class with private members
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE**](nlohmann_define_derived_type.md) - serialize/deserialize a derived
class
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT**](nlohmann_define_derived_type.md) - serialize/deserialize
a derived class; uses default values
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE**](nlohmann_define_derived_type.md) - serialize a derived
class
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a non-derived class
with private members; uses custom names
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a
non-derived class with private members; uses default values; uses custom names
- [**NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize a non-derived class
with private members; uses custom names
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a non-derived
class; uses custom names
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a
non-derived class; uses default values; uses custom names
- [**NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize a
non-derived class; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a derived class
with private members; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a
derived class with private members; uses default values; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize a derived
class with private members; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize a derived
class; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize/deserialize
a derived class; uses default values; uses custom names
- [**NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES**](nlohmann_define_type_with_names.md) - serialize a derived
class; uses custom names
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