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std::map<Key,T,Compare,Allocator>::contains

bool contains( const Key& key ) const;
 (1) (since C++20) 
template< class K > bool contains( const K& x ) const;
 (2) (since C++20)
1) Checks if there is an element with key equivalent to key in the container.
2) Checks if there is an element with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of Key.

Parameters

key - key value of the element to search for
x - a value of any type that can be transparently compared with a key

Return value

true if there is such an element, otherwise false.

Complexity

Logarithmic in the size of the container.

Example

#include <iostream>
#include <map>
 
int main()
{
    std::map<int,char> example = {{1,'a'},{2,'b'}};
 
    for(int x: {2, 5}) {
        if(example.contains(x)) {
            std::cout << x << ": Found\n";
        } else {
            std::cout << x << ": Not found\n";
        }
    }
}

Output:

2: Found
5: Not found

See also

finds element with specific key
(public member function)
returns the number of elements matching specific key
(public member function)
returns range of elements matching a specific key
(public member function)

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