// (1) size_type count(const typename object_t::key_type& key) const; // (2) template<typename KeyType> size_type count(KeyType&& key) const;
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).KeyType
is comparable with #!cpp typename object_t::key_type
and #!cpp typename object_comparator_t::is_transparent
denotes a type.KeyType
: A type for an object key other than json_pointer
that is comparable with string_t
using object_comparator_t
. This can also be a string view (C++17).
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 “Example: (1) count number of elements”
The example shows how `count()` is used. ```cpp --8<-- "examples/count__object_t_key_type.cpp" ``` Output: ```json --8<-- "examples/count__object_t_key_type.output" ```
??? example “Example: (2) count number of elements using string_view”
The example shows how `count()` is used. ```cpp --8<-- "examples/count__keytype.c++17.cpp" ``` Output: ```json --8<-- "examples/count__keytype.c++17.output" ```
key
type to KeyType&&
in version 3.11.0.