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std::unordered_set contains() method

// (1) Const version only
bool contains( const Key& key ) const;

// (2) Const version only
template< class K >
bool contains( const K& x ) const;
  • (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 elements to count
  • 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

Average case, constant - O(1).
Worst case, linear in size of the container - O(size()).

Exceptions

(none)

Example

Main.cpp
#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
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Hover to see the original license.

std::unordered_set contains() method

// (1) Const version only
bool contains( const Key& key ) const;

// (2) Const version only
template< class K >
bool contains( const K& x ) const;
  • (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 elements to count
  • 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

Average case, constant - O(1).
Worst case, linear in size of the container - O(size()).

Exceptions

(none)

Example

Main.cpp
#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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.