Niels Lohmann
63c10a51fc
* Review and extend the documentation, and check it in CI A review of all documentation pages found factual errors, dead links, missing cross-references, and gaps in examples. This fixes them and adds checks so the same problems are caught automatically. Fixes: - wrong signatures and version histories (operator!= C++20 member, binary() subtype type, get<PointerType>(), JSON_NO_THREAD_LOCAL, ...) - stale descriptions (number parsing since #5283, UBJSON table, SAX example that no longer compiled, tsl::ordered_map advice) - dead internal and external links; repology.org badges (the domain is suspended) replaced by badges that query the registries directly - deprecation notes link the migration guide; the guide itself fixed Additions: - "See also" sections, cross-references, 25 runnable examples, 12 Mermaid diagrams, new API pages for json_pointer::operator<=> and byte_container_with_subtype::operator==/!= - landing page, guides for untrusted input and performance - "unreleased" badge after versions newer than the latest release Checks: - strict documentation build (broken links/anchors fail it); CI and the publish workflow fetch the full history the build needs - weekly external link check, Mermaid syntax check in CI - check_structure.py: example titles, heading levels, alt texts, header links, docset index coverage; its unused-example check works again - all examples produce the same output on every platform Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Keep the customer links that could not be fixed A dead link on the customers page is still the evidence of where the use of the library was documented. Keep the original URLs of the entries without a working replacement (Marne, Cisco Webex Desk Camera, Philips Hue, CyberArk) and exclude exactly these URLs from the link check. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct the duplicate-key recipe's claim about SAX positions The SAX interface's key() receives no position either; only parse_error() does. Also note that the recipe does not report the path to the repeated key (see discussion #5085). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Say the library is available as a single header and mention json_fwd.hpp Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct documentation errors found while hunting for bugs - patch/patch_inplace: list the JSON pointer errors parse_error.106-109 and out_of_range.402/404, and quote the actual parse_error.105 message. - unflatten: list parse_error.106/107/108 and out_of_range.404. - to_bson: list out_of_range.415 (binary subtype above 255) and note that 412 and 415 are new in 3.13.0. - to_string: state that string_t must be convertible to std::string, also in the StringType requirements table. - JSON Lines: a `while (input >> j)` loop also throws after the last value for concatenated JSON values; show a loop that works for both. - BON8: a string gets 0xFF only if nothing follows it in the message; a string at the end of an array or object is ended by 0xFE. - custom_string_type.hpp: add operator+=(char), which the "Always required" list asks for (json_pointer::to_string, flatten, unflatten, and diff did not compile), and an ADL int_to_string for diff and items. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Cache the release headers with functools.lru_cache Codacy (Pylint) flagged the mutable default argument that header() used as its cache. functools.lru_cache keeps the same memoization without it. The script's output is unchanged. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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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_BRACE_INIT_COPY_SEMANTICS
When defined to 1, single-element brace initialization of a basic_json value (e.g., #!cpp json j{value};) is
treated as a copy/move of the element rather than wrapping it in a single-element array. The default value is 0, which
preserves the existing behavior.
See full documentation of JSON_BRACE_INIT_COPY_SEMANTICS.
JSON_CATCH_USER(exception)
This macro overrides #!cpp 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_DIAGNOSTIC_POSITIONS
When enabled, two new member functions start_pos() and
end_pos() are added to basic_json values. If the value
was created by calling theparse function, then these functions allow querying the byte
positions of the value in the input it was parsed from. The byte positions are also used in exceptions to help locate
errors.
The diagnostics positions can also be controlled with the CMake option
JSON_Diagnostic_Positions (OFF by default) which sets
JSON_DIAGNOSTIC_POSITIONS accordingly.
See full documentation of JSON_DIAGNOSTIC_POSITIONS
JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20, JSON_HAS_CPP_23, JSON_HAS_CPP_26
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.
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_DISABLE_TUPLE_REFERENCE_CONVERSION
When defined to 1, a JSON value can no longer be created from a one-element std::tuple holding a reference to a JSON
value, such as the result of std::forward_as_tuple(j). This lets std::tuple convert such tuples element-wise.
See full documentation of JSON_DISABLE_TUPLE_REFERENCE_CONVERSION.
JSON_NO_AUTOMATIC_UDLS
When defined, <nlohmann/json.hpp> does not include <nlohmann/json_literals.hpp> with the user-defined string literals
operator""_json and operator""_json_pointer. This reduces the compile time of translation units that do not use
them, because the literals instantiate the parser in every translation unit that includes them. Include
<nlohmann/json_literals.hpp> where the literals are needed.
See full documentation of JSON_NO_AUTOMATIC_UDLS.
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_NO_THREAD_LOCAL
When defined, the library does not use #!cpp thread_local storage. Copying a value and comparing two values then
always avoid the call stack rather than descending into a bounded number of levels first, which is slower but yields the
same values and the same comparisons.
See full documentation of JSON_NO_THREAD_LOCAL.
JSON_PRECISE_STREAM_POSITION
When defined to 1, operator>> and non-strict
sax_parse leave an input stream positioned right after the parsed value, instead of
also consuming the character that terminates a number. The default value is 0, which preserves the existing behavior;
this is planned to become the default in version 4.0.0.
See full documentation of JSON_PRECISE_STREAM_POSITION.
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 using 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_STRICT_NUL_HANDLING
When defined to 1, a '\0' (NUL) byte anywhere in the input is rejected with parse_error.101, like any other
unexpected byte, instead of being silently treated as end of input (see the
FAQ entry for background). The default value is 0, which preserves the
existing behavior; this is planned to become the default in version 4.0.0.
The strict handling can also be enabled with the CMake option
JSON_StrictNulHandling (OFF by default) which sets
JSON_STRICT_NUL_HANDLING accordingly.
See full documentation of JSON_STRICT_NUL_HANDLING.
JSON_THROW_USER(exception)
This macro overrides #!cpp 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 #!cpp 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.
JSON_USE_GLOBAL_UDLS
When defined to 1 (default), the user-defined string literals operator""_json and operator""_json_pointer are
placed into the global namespace instead of nlohmann::literals::json_literals.
See full documentation of JSON_USE_GLOBAL_UDLS.
JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
When defined to 1, the library restores the legacy behavior in which a discarded value compared equal to itself. This
behavior is deprecated and switched off (0) by
default.
See full documentation of JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON.
JSON_USE_SIMDUTF
When defined, UTF-8 validation of JSON strings read from contiguous byte input is delegated to the simdutf library instead of the built-in scalar validator. This is an opt-in external dependency and is not defined by default.
See full documentation of JSON_USE_SIMDUTF.
NLOHMANN_DEFINE_TYPE_*(...), NLOHMANN_DEFINE_DERIVED_TYPE_*(...)
The library defines 12 macros to simplify the serialization/deserialization of types. See the page on arbitrary type conversion for a detailed discussion.
NLOHMANN_JSON_NAMESPACE, NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END, NLOHMANN_JSON_NAMESPACE_NO_VERSION
These macros relate to the versioned, inline nlohmann namespace:
NLOHMANN_JSON_NAMESPACEevaluates to the full name of thenlohmannnamespace (including the inline ABI namespace).NLOHMANN_JSON_NAMESPACE_BEGIN/NLOHMANN_JSON_NAMESPACE_ENDopen and close the namespace (for example, to add specializations).NLOHMANN_JSON_NAMESPACE_NO_VERSION, when defined to1, omits the version component from the inline namespace.
See the nlohmann Namespace page, and the full documentation of
NLOHMANN_JSON_NAMESPACE,
NLOHMANN_JSON_NAMESPACE_BEGIN / NLOHMANN_JSON_NAMESPACE_END, and
NLOHMANN_JSON_NAMESPACE_NO_VERSION.
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.
A strict variant NLOHMANN_JSON_SERIALIZE_ENUM_STRICT throws an
exception on undefined input instead of falling back to the first mapping.
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.