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std::unordered_map::contains(3) C++ Standard Libary std::unordered_map::contains(3)


std::unordered_map::contains - std::unordered_map::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 Hash::is_transparent and
KeyEqual::is_transparent are valid and each denotes a type. 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 - 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.


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


// Run this code

#include <iostream>
#include <unordered_map>

int main()
std::unordered_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";


2: Found
5: Not found

See also

find finds element with specific key
(C++11) (public member function)
count returns the number of elements matching specific key
(C++11) (public member function)
equal_range returns range of elements matching a specific key
(C++11) (public member function)