template<typename KeyT> size_type count(KeyT&& key) const;
Returns the number of elements with key key. If ObjectType is the default std::map type, the return value will always be 0 (key was not found) or 1 (key was found).
KeyT : A type for an object key.
key (in) : key value of the element to count.
Number of elements with key key. If the JSON value is not an object, the return value will be 0.
Strong exception safety: if an exception occurs, the original value stays intact.
Logarithmic in the size of the JSON object.
This method always returns 0 when executed on a JSON type that is not an object.
??? example
The example shows how `count()` is used. ```cpp --8<-- "examples/count.cpp" ``` Output: ```json --8<-- "examples/count.output" ```