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api/basic_json/find/index.md

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+# nlohmann::basic_json::find
+
+```
+// (1)
+iterator find(const typename object_t::key_type& key);
+const_iterator find(const typename object_t::key_type& key) const;
+
+// (2)
+template<typename KeyType>
+iterator find(KeyType&& key);
+template<typename KeyType>
+const_iterator find(KeyType&& key) const;
+```
+
+1. Finds an element in a JSON object with a key equivalent to `key`. If the element is not found or the JSON value is not an object, `end()` is returned.
+1. See 1. This overload is only available if `KeyType` is comparable with `typename object_t::key_type` and `typename object_comparator_t::is_transparent` denotes a type.
+
+## Template parameters
+
+`KeyType` : A type for an object key other than [`json_pointer`](https://json.nlohmann.me/api/json_pointer/index.md) that is comparable with [`string_t`](https://json.nlohmann.me/api/basic_json/string_t/index.md) using [`object_comparator_t`](https://json.nlohmann.me/api/basic_json/object_comparator_t/index.md). This can also be a string view (C++17).
+
+## Parameters
+
+`key` (in) : key value of the element to search for.
+
+## Return value
+
+Iterator to an element with a key equivalent to `key`. If no such element is found or the JSON value is not an object, a past-the-end iterator (see `end()`) is returned.
+
+## Exception safety
+
+Strong exception safety: if an exception occurs, the original value stays intact.
+
+## Complexity
+
+Logarithmic in the size of the JSON object.
+
+## Notes
+
+This method always returns `end()` when executed on a JSON type that is not an object.
+
+## Examples
+
+Example: (1) find object element by key
+
+The example shows how `find()` is used.
+
+```
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON object
+    json j_object = {{"one", 1}, {"two", 2}};
+
+    // call find
+    auto it_two = j_object.find("two");
+    auto it_three = j_object.find("three");
+
+    // print values
+    std::cout << std::boolalpha;
+    std::cout << "\"two\" was found: " << (it_two != j_object.end()) << '\n';
+    std::cout << "value at key \"two\": " << *it_two << '\n';
+    std::cout << "\"three\" was found: " << (it_three != j_object.end()) << '\n';
+}
+```
+
+Output:
+
+```
+"two" was found: true
+value at key "two": 2
+"three" was found: false
+```
+
+Example: (2) find object element by key using string_view
+
+The example shows how `find()` is used.
+
+```
+#include <iostream>
+#include <string_view>
+#include <nlohmann/json.hpp>
+
+using namespace std::string_view_literals;
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON object
+    json j_object = {{"one", 1}, {"two", 2}};
+
+    // call find
+    auto it_two = j_object.find("two"sv);
+    auto it_three = j_object.find("three"sv);
+
+    // print values
+    std::cout << std::boolalpha;
+    std::cout << "\"two\" was found: " << (it_two != j_object.end()) << '\n';
+    std::cout << "value at key \"two\": " << *it_two << '\n';
+    std::cout << "\"three\" was found: " << (it_three != j_object.end()) << '\n';
+}
+```
+
+Output:
+
+```
+"two" was found: true
+value at key "two": 2
+"three" was found: false
+```
+
+## See also
+
+- [count](https://json.nlohmann.me/api/basic_json/count/index.md) returns the number of occurrences of a key
+- [contains](https://json.nlohmann.me/api/basic_json/contains/index.md) checks whether a key exists
+
+## Version history
+
+1. Added in version 3.11.0.
+1. Added in version 1.0.0. Changed to support comparable types in version 3.11.0.