mirror of https://github.com/nlohmann/json.git synced 2026-10-13 04:15:17 +00:00

Files

Niels Lohmann 63c10a51fc Review and extend the documentation, and check it in CI (#5638 )

* 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>

2026-10-02 11:32:15 +02:00

2.0 KiB

Raw Blame History

nlohmann::json_pointer::operator<=>

// since C++20
class json_pointer {
    template<typename RefStringTypeRhs>
    std::strong_ordering operator<=>(const json_pointer<RefStringTypeRhs>& rhs) const noexcept; // *NOPAD*
};

3-way compares two JSON pointers by lexicographically comparing their sequences of reference tokens: corresponding reference tokens are compared with string_t's own operator<=>, and the first pair of tokens that differs determines the result. If all corresponding reference tokens compare equal, the JSON pointer with fewer reference tokens is ordered first.

Template parameters

RefStringTypeRhs: the string type of the right-hand side JSON pointer

Parameters

rhs (in): JSON pointer to compare *this with

Return value

the std::strong_ordering of the 3-way comparison of *this and rhs

Exception safety

No-throw guarantee: this function never throws exceptions.

Complexity

Linear in the number of reference tokens.

Notes

!!! note "Ordering enables use as an associative container key"

Together with [`operator==`](operator_eq.md), `operator<=>` makes `json_pointer` a `LessThanComparable` type, so
it can be used as the key type of ordered associative containers such as `std::map` or `std::set`.

!!! note "Before C++20"

Without C++20's three-way comparison, `json_pointer` provides a non-member `operator<` instead, which orders JSON
pointers the same way. JSON pointers can therefore be used as keys of ordered associative containers with any
supported C++ standard.

Examples

??? example

The example demonstrates 3-way comparing JSON pointers.

```cpp
--8<-- "examples/json_pointer__operator_spaceship.c++20.cpp"
```

Output:

```
--8<-- "examples/json_pointer__operator_spaceship.c++20.output"
```

Version history

Added in version 3.11.2.

2.0 KiB Raw Blame History