1# <small>nlohmann::basic_json::</small>count 2 3```cpp 4// (1) 5size_type count(const typename object_t::key_type& key) const; 6 7// (2) 8template<typename KeyType> 9size_type count(KeyType&& key) const; 10``` 11 121. Returns the number of elements with key `key`. If `ObjectType` is the default `std::map` type, the return value will 13 always be `0` (`key` was not found) or `1` (`key` was found). 142. See 1. This overload is only available if `KeyType` is comparable with `#!cpp typename object_t::key_type` and 15 `#!cpp typename object_comparator_t::is_transparent` denotes a type. 16 17## Template parameters 18 19`KeyType` 20: A type for an object key other than [`json_pointer`](../json_pointer/index.md) that is comparable with 21 [`string_t`](string_t.md) using [`object_comparator_t`](object_comparator_t.md). 22 This can also be a string view (C++17). 23 24## Parameters 25 26`key` (in) 27: key value of the element to count. 28 29## Return value 30 31Number of elements with key `key`. If the JSON value is not an object, the return value will be `0`. 32 33## Exception safety 34 35Strong exception safety: if an exception occurs, the original value stays intact. 36 37## Complexity 38 39Logarithmic in the size of the JSON object. 40 41## Notes 42 43This method always returns `0` when executed on a JSON type that is not an object. 44 45## Examples 46 47??? example "Example: (1) count number of elements" 48 49 The example shows how `count()` is used. 50 51 ```cpp 52 --8<-- "examples/count__object_t_key_type.cpp" 53 ``` 54 55 Output: 56 57 ```json 58 --8<-- "examples/count__object_t_key_type.output" 59 ``` 60 61??? example "Example: (2) count number of elements using string_view" 62 63 The example shows how `count()` is used. 64 65 ```cpp 66 --8<-- "examples/count__keytype.c++17.cpp" 67 ``` 68 69 Output: 70 71 ```json 72 --8<-- "examples/count__keytype.c++17.output" 73 ``` 74 75## Version history 76 771. Added in version 3.11.0. 782. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0. 79