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Niels Lohmann 52b72b5684 Improve documentation: byte layouts, release pages, See also, dark-mode images (#5906 )

- Make the iterator range illustrations legible in dark mode (prefers-color-scheme
  rules inside the SVGs).
- Add a "Byte layout" section with a color-coded byte table to each binary format
  page (BJData, BON8, BSON, CBOR, MessagePack, UBJSON), and highlight the smallest
  size per file in the comparison table.
- Add "See also" sections to the overview pages that lacked one.
- Split the release notes into one page per release, grouped by minor version on
  the overview page, with an "API changes" section per release generated from the
  API pages' version histories (hooks/api_changes.py).
- Fact-check the release notes and version histories against the release tags and
  correct wrong or misleading entries (e.g., json_serializer 2.1.0, merge_patch
  3.1.0, items, count, operator[], to_bjdata, std::string_view key support).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-10-24 17:57:44 +02:00

2.1 KiB

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nlohmann::basic_json::merge_patch

void merge_patch(const basic_json& apply_patch);

The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of modifications to a target resource's content. This function applies a merge patch to the current JSON value.

The function implements the following algorithm from Section 2 of RFC 7396 (JSON Merge Patch):

define MergePatch(Target, Patch):
  if Patch is an Object:
    if Target is not an Object:
      Target = {} // Ignore the contents and set it to an empty Object
    for each Name/Value pair in Patch:
      if Value is null:
        if Name exists in Target:
          remove the Name/Value pair from Target
      else:
        Target[Name] = MergePatch(Target[Name], Value)
    return Target
  else:
    return Patch

Thereby, Target is the current object; that is, the patch is applied to the current value.

Parameters

apply_patch (in): the patch to apply

Exception safety

Basic guarantee: if an exception is thrown during the operation, the JSON value may be partially modified.

Complexity

Linear in the lengths of apply_patch.

Notes

apply_patch may be #!cpp *this itself or refer to a value contained in #!cpp *this (for example, a subobject returned by #!cpp (*this)[key]); it is read as it was when merge_patch() was called, before any modification of #!cpp *this.

Examples

??? example

The following code shows how a JSON Merge Patch is applied to a JSON document.
 
```cpp
--8<-- "examples/merge_patch.cpp"
```

Output:

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

Version history

Added in version 3.1.0.
Fixed use of freed or relocated memory when apply_patch is #!cpp *this or refers to a value contained in #!cpp *this, in version 3.13.0.

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