std::unordered_set<Key,Hash,KeyEqual,Allocator>::contains
From cppreference.com
< cpp | container | unordered set
| 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.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_set> int main() { std::unordered_set<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
| (C++11) |
finds element with specific key (public member function) |
| (C++11) |
returns the number of elements matching specific key (public member function) |
| (C++11) |
returns range of elements matching a specific key (public member function) |