nlohmann::basic_json::flatten

basic_json flatten() const;

The function creates a JSON object whose keys are JSON pointers (see RFC 6901) and whose values are all primitive (see is_primitive() for more information). The original JSON value can be restored using the unflatten() function.

Return value

an object that maps JSON pointers to primitive values

Exception safety

Strong exception safety: if an exception occurs, the original value stays intact.

Complexity

Linear in the size of the JSON value.

Notes

Empty objects and arrays are flattened to #!json null and will not be reconstructed correctly by the unflatten() function.

Examples

??? example "Example: flatten a JSON object"

The following code shows how a JSON object is flattened to an object whose keys consist of JSON pointers.

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

Output:

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

??? example "Example: empty objects and arrays are flattened to #!json null"

The following code shows that an empty object and an empty array are both flattened to `#!json null`, and that
`unflatten()` restores them as `#!json null` rather than as empty containers.

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

Output:

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

Version history

Added in version 2.0.0.

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