4703dd57e5
Conflicts: doc/mkdocs/docs/api/basic_json/contains.md doc/mkdocs/docs/api/basic_json/find.md include/nlohmann/json.hpp single_include/nlohmann/json.hpp test/src/unit-regression2.cpp
58 lines
1.2 KiB
Markdown
58 lines
1.2 KiB
Markdown
# <small>nlohmann::basic_json::</small>count
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```cpp
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template<typename KeyT>
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size_type count(const KeyT& key) const;
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```
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Returns the number of elements with key `key`. If `ObjectType` is the default `std::map` type, the return value will
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always be `0` (`key` was not found) or `1` (`key` was found).
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## Template parameters
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`KeyT`
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: A type for an object key that is less-than comparable with `string_t`. This can also be a string literal or a string
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view (C++17).
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## Parameters
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`key` (in)
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: key value of the element to count.
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## Return value
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Number of elements with key `key`. If the JSON value is not an object, the return value will be `0`.
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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 `0` when executed on a JSON type that is not an object.
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## Examples
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??? example
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The example shows how `count()` is used.
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```cpp
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--8<-- "examples/count.cpp"
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```
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Output:
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```json
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--8<-- "examples/count.output"
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```
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## Version history
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- Added in version 1.0.0.
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- Extended template `KeyT` in version 3.10.5 to also support `std::string_view`.
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