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std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::contains

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C++
 
Containers library
 
std::unordered_multimap
Member types
Member functions
Non-member functions
(until C++20)
Deduction guides (C++17)
 
bool contains( const Key& key ) const;
 (1) (since {std})
(constexpr since C++26)
template< class K >
bool contains( const K& x ) const;
 (2) (since {std})
(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 Hash and KeyEqual are both transparent. This assumes that such Hash is callable with both K and Key type, and that the KeyEqual is transparent, which, together, allows calling this function without constructing an instance of Key.

Contents

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

Constant on average, worst case linear in the size of the container.

Example

Run this code
#include <iostream>
#include <unordered multimap>
 
int main()
{
    std::unordered multimap<int> example{1, 2, 3, 4};
 
    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) [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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