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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

5.5 KiB

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nlohmann::basic_json::patch

basic_json patch(const basic_json& json_patch) const;

JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JSON document. With this function, a JSON Patch is applied to the current JSON value by executing all operations from the patch.

Parameters

json_patch (in): JSON patch document

Return value

patched document

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

Exceptions

Throws parse_error.104 if the JSON patch does not consist of an array of objects.
Throws parse_error.105 if the JSON patch is malformed (e.g., mandatory attributes are missing); example: "operation 'add' must have member 'path'".
Throws out_of_range.401 if an array index is out of range.
Throws parse_error.106 if an array index in a "path" or "from" member begins with '0'; example: "array index '01' must not begin with '0'".
Throws parse_error.107 if a "path" or "from" member is not empty and does not begin with a slash (/); example: "JSON pointer must be empty or begin with '/' - was: 'a'".
Throws parse_error.108 if a tilde (~) in a "path" or "from" member is not followed by 0 or 1; example: "escape character '~' must be followed with '0' or '1'".
Throws parse_error.109 if an array index in a "path" or "from" member is not a number; example: "array index 'foo' is not a number".
Throws out_of_range.402 if the array index - is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: "array index '-' (3) is out of range".
Throws out_of_range.403 if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: "key baz not found".
Throws out_of_range.404 if a reference token of a JSON pointer inside the patch cannot be resolved, e.g., - in a "remove" operation or 1a for an array; example: "unresolved reference token '-'".
Throws out_of_range.405 if JSON pointer has no parent ("add", "remove", "move")
Throws out_of_range.411 if an "add" operation's target location has a parent that is neither an object nor an array.
Throws out_of_range.413 if a "remove" operation's target location has a parent that is neither an object nor an array.
Throws out_of_range.414 if a "move" operation's "from" location is a proper prefix of its "path" location.
Throws other_error.501 if "test" operation was unsuccessful.

Complexity

Linear in the size of the JSON value and the length of the JSON patch. As usually the patch affects only a fraction of the JSON value, the complexity can usually be neglected.

Notes

The application of a patch is atomic: Either all operations succeed and the patched document is returned or an exception is thrown. In any case, the original value is not changed: the patch is applied to a copy of the value.

Examples

??? example "Example: apply a JSON patch"

The following code shows how a JSON patch is applied to a value.
 
```cpp
--8<-- "examples/patch.cpp"
```

Output:

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

??? example "Example: out_of_range.414 exception"

The following code shows how a "move" operation whose "from" location is a proper prefix of its "path" location is
rejected, and how the original document is left unchanged because the patch is applied to a copy.

```cpp
--8<-- "examples/patch__exception.cpp"
```

Output:

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

Version history

Added in version 2.0.0.
Added out_of_range.411 and stopped relying on an internal assertion when an "add" operation's target location has a non-object/non-array parent in version 3.13.0.
Added out_of_range.413 and stopped silently ignoring a "remove" operation whose target location has a non-object/non-array parent in version 3.13.0.
Added out_of_range.414 and rejected a "move" operation whose "from" location is a proper prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0.

5.5 KiB Raw Blame History