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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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Features
This section describes the features of the library in detail. If you are new to the library, the pages below are roughly ordered along a typical workflow: create or parse a value, access and modify it, convert it to and from your own C++ types, and finally serialize it again.
Creating and reading values
- Creating JSON values — build values from literals, initializer lists, and STL containers, and
understand the
#!cpp {}vs.#!cpp []ambiguity. - Parsing — read a JSON value from a string, file, or stream, including JSON Lines, callbacks, the SAX interface, error handling, and parsing untrusted input.
- Comments and trailing commas — opt-in relaxations of the JSON grammar.
Accessing and modifying values
- Element access — unchecked (
operator[]), checked (at), and access with a default value. - JSON Pointer — address values deep inside a document with RFC 6901 pointers.
- Iterators — traverse arrays and objects.
- Modifying values — add, update, merge, and remove elements.
- JSON Patch and Diff and JSON Merge Patch — apply and compute structured changes.
Converting to and from C++ types
- Converting values — get values out with
get/get_to, and understand implicit conversions. - Arbitrary types conversions — teach the library about your own structs and classes.
- Specializing enum conversion — map enums to strings instead of integers.
Serializing values
- Serialization — turn a value back into JSON text with
dump, including pretty-printing and handling of non-ASCII and invalid UTF-8. - Binary formats — encode values more compactly as BJData, BON8, BSON, CBOR, MessagePack, or UBJSON.
- Binary values — store and exchange raw byte sequences.
How values are stored and configured
- Types and number handling — how JSON types map to C++ types and how numbers are treated.
- Template parameter requirements — what a type passed as one of
basic_json's template parameters has to provide. - Object order — keep insertion order with
ordered_json. - Performance — practical advice on parsing, memory use, serialization, and compile times.
- Runtime assertions, supported macros, the
nlohmannnamespace, and C++ modules — build-time and runtime configuration.
!!! tip "Looking for a specific function?"
This section gives conceptual overviews. For the precise signature, parameters, and return value of a function, see
the [API Documentation](../api/basic_json/index.md).