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Niels Lohmann 526b6d3fd6 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>

2026-09-29 17:05:35 +02:00

3.2 KiB

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nlohmann::json_pointer

template<typename RefStringType>
class json_pointer;

A JSON pointer defines a string syntax for identifying a specific value within a JSON document. It can be used with functions at and operator[]. Furthermore, JSON pointers are the base for JSON patches.

Template parameters

RefStringType: the string type used for the reference tokens making up the JSON pointer

!!! warning "Deprecation"

For backwards compatibility `RefStringType` may also be a specialization of [`basic_json`](../basic_json/index.md)
in which case `string_t` will be deduced as [`basic_json::string_t`](../basic_json/string_t.md). This feature is
deprecated and may be removed in a future major version.

See the [migration guide](../../integration/migration_guide.md#json-pointers) for how to update existing code.

A JSON pointer is internally a sequence of reference tokens. front, pop_front, and push_front act on the first reference token, whereas back, pop_back, and push_back act on the last one. parent_pointer returns a new JSON pointer with the last reference token removed (like a non-mutating pop_back):

flowchart LR
    A["a"] --> B["b"] --> C["c"]

    front["front() / pop_front() / push_front()"] -.-> A
    back["back() / pop_back() / push_back()"] -.-> C
    parent["parent_pointer() returns /a/b"] -.-> B

The diagram shows the reference tokens of the JSON pointer /a/b/c.

Member types

string_t - the string type used for the reference tokens

Member functions

(constructor)
to_string - return a string representation of the JSON pointer
operator string_t - return a string representation of the JSON pointer (deprecated)
operator== - compare: equal
operator!= - compare: not equal
operator<=> - compare: 3-way (C++20)
operator/= - append to the end of the JSON pointer
operator/ - create JSON Pointer by appending
parent_pointer - returns the parent of this JSON pointer
pop_back - remove the last reference token
back - return last reference token
push_back - append an unescaped token at the end of the pointer
pop_front - remove the first reference token
front - return first reference token
push_front - append an unescaped token at the start of the pointer
empty - return whether the pointer points to the root document

Literals

operator""_json_pointer - user-defined string literal for JSON pointers

Version history

Added in version 2.0.0.
Changed template parameter from basic_json to string type in version 3.11.0.

3.2 KiB Raw Blame History