mirror of
https://github.com/nlohmann/json.git
synced 2024-12-17 07:27:49 +08:00
57 lines
1.1 KiB
Markdown
57 lines
1.1 KiB
Markdown
|
# basic_json::contains
|
||
|
|
|
||
|
|
```cpp
|
||
|
|
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.
|