basic_json::contains

template<typename KeyT>
bool contains(KeyT && key) const;

Check whether an element exists in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, #!cpp false is returned.

Template parameters

KeyT: A type for an object key other than basic_json::json_pointer.

Parameters

key (in): key value to check its existence.

Return value

#!cpp true if an element with specified key exists. If no such element with such key is found or the JSON value is not an object, #!cpp false is returned.

Exception safety

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

Complexity

Logarithmic in the size of the JSON object.

Notes

This method always returns #!cpp false when executed on a JSON type that is not an object.

Example

??? example

The example shows how `contains()` is used.

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

Output:

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

Version history

Added in version 3.6.0.

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