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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

2.8 KiB

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nlohmann::basic_json::operator<=

// until C++20
bool operator<=(const_reference lhs, const_reference rhs) noexcept;   // (1)

template<typename ScalarType>
bool operator<=(const_reference lhs, const ScalarType rhs) noexcept;  // (2)

template<typename ScalarType>
bool operator<=(ScalarType lhs, const const_reference rhs) noexcept;  // (2)

Compares whether one JSON value lhs is less than or equal to another JSON value rhs according to the following rules:
- The comparison always yields #!cpp false if (1) either operand is discarded, or (2) either operand is NaN and the other operand is either NaN or any other number.
- Otherwise, returns the result of #!cpp !(rhs < lhs) (see operator<).
Compares whether a JSON value is less than or equal to a scalar or a scalar is less than or equal to a JSON value by converting the scalar to a JSON value and comparing both JSON values according to 1.

Template parameters

ScalarType: a scalar type according to std::is_scalar<ScalarType>::value

Parameters

lhs (in): first value to consider
rhs (in): second value to consider

Return value

whether lhs is less than or equal to rhs

Exception safety

No-throw guarantee: this function never throws exceptions.

Complexity

Linear.

Notes

!!! note "Comparing NaN"

`NaN` values are unordered within the domain of numbers.
The following comparisons all yield `#!cpp false`:
  1. Comparing a `NaN` with itself.
  2. Comparing a `NaN` with another `NaN`.
  3. Comparing a `NaN` and any other number.

!!! note "Operator overload resolution"

Since C++20 overload resolution will consider the _rewritten candidate_ generated from
[`operator<=>`](operator_spaceship.md).

!!! warning "Deprecation"

If [`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](../macros/json_use_legacy_discarded_value_comparison.md) is
defined to `1`, the library declares a member `#!cpp bool operator<=(const_reference rhs) const noexcept` in
C++20 mode to emulate the legacy comparison of discarded values. This member is deprecated since version 3.11.0,
together with the legacy comparison behavior.

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

Examples

??? example

The example demonstrates comparing several JSON types.
    
```cpp
--8<-- "examples/operator__lessequal.cpp"
```

Output:

```json
--8<-- "examples/operator__lessequal.output"
```

Version history

Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.

2.8 KiB Raw Blame History