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

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C++
Containers library
std::map
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
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

Run this code 
#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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