57 lines
1.1 KiB
Markdown
57 lines
1.1 KiB
Markdown
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# basic_json::contains
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```cpp
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template<typename KeyT>
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bool contains(KeyT && key) const;
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```
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Check whether an element exists in a JSON object with key equivalent to `key`. If the element is not found or the JSON
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value is not an object, `#!cpp false` is returned.
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## Template parameters
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`KeyT`
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: A type for an object key other than `basic_json::json_pointer`.
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## Parameters
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`key` (in)
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: key value to check its existence.
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## Return value
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`#!cpp true` if an element with specified `key` exists. If no such element with such key is found or the JSON value is
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not an object, `#!cpp false` is returned.
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## Exception safety
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Strong exception safety: if an exception occurs, the original value stays intact.
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## Complexity
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Logarithmic in the size of the JSON object.
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## Notes
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This method always returns `#!cpp false` when executed on a JSON type that is not an object.
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## Example
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??? example
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The example shows how `contains()` is used.
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```cpp
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--8<-- "examples/contains.cpp"
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```
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Output:
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```json
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--8<-- "examples/contains.output"
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```
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## Version history
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- Added in version 3.6.0.
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