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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../ranges/../container/map/contains.html below:

std::map<Key,T,Compare,Allocator>::contains - cppreference.com

bool contains( const Key& key ) const;

(1) (since C++20)
(constexpr since C++26)

template< class K > bool contains( const K& x ) const;

(2) (since C++20)
(constexpr since C++26)

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 x.

This overload participates in overload resolution only if

Compare

transparent

. It allows calling this function without constructing an instance of

Key

[edit] Parameters key - key value of the element to search for x - a value of any type that can be transparently compared with a key [edit] Return value

true if there is such an element, otherwise false.

[edit] Complexity

Logarithmic in the size of the container.

[edit] 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:

[edit] See also finds element with specific key
(public member function) [edit] returns the number of elements matching specific key
(public member function) [edit] returns range of elements matching a specific key
(public member function) [edit]

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