Niels Lohmann
ccc005c012
- Discarded values: the legacy macro only changes <= and >=; != is true by default - Out-of-range numbers are rejected while parsing, not stored as NaN - merge_diff round trip: point to the ordered_json caveat - ensure_ascii example shows the escaped output - out_of_range.405 is thrown for "remove"/"move" on the root, not "add" - CBOR stores binary subtypes as tags - Integer/float comparison uses exact values, not conversion - diff, flatten, and the binary writers are depth-bounded - FAQ: max_digits10 for serialization, trailing commas are supported - out_of_range.407 is still thrown by to_bon8 - FetchContent_MakeAvailable needs CMake 3.14 - json_fwd.hpp contents, operator< link, RFC 7396 for merge patch - README: dump() wording, merge_diff, MSYS2/build2, patch comment typos, operator[] link, embedded CMake example aligned with the docs Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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JSON Merge Patch
The library supports JSON Merge Patch (RFC 7396) as a patch format. 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.
Instead of using JSON Pointer to specify values to be manipulated, it describes the changes using a syntax that closely mimics the document being modified. Unlike JSON Patch, a JSON Merge Patch cannot express every kind of change (e.g., it cannot reorder array elements or remove a specific array element), but it is easier to read and write for object-shaped documents.
The function merge_diff creates a merge patch that changes one JSON value into
another.
!!! tip "Not a general deep merge"
A merge patch is not a general deep merge: a `#!json null` value in the patch deletes the key from the target.
To merge two objects recursively (e.g., defaults and user settings), use
[`update`](../api/basic_json/update.md) with `merge_objects` set to `#!cpp true`; see
[Merging objects](modifying_values.md#merging-objects).
??? 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"
```
See also
- JSON Patch and Diff - a more expressive alternative that describes a sequence of operations
- JSON Pointer - the addressing scheme used by JSON Patch
- Function
merge_patch - Function
merge_diff - Function
update- merge objects, optionally recursively