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

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

span (C++20)

 

std::unordered_multimap

Member functions

unordered_multimap::unordered_multimap

unordered_multimap::~unordered_multimap

unordered_multimap::operator=

unordered_multimap::get_allocator

Iterators

unordered_multimap::beginunordered_multimap::cbegin

unordered_multimap::endunordered_multimap::cend

Capacity

unordered_multimap::empty

unordered_multimap::size

unordered_multimap::max_size

Modifiers

unordered_multimap::clear

unordered_multimap::insert

unordered_multimap::emplace

unordered_multimap::emplace_hint

unordered_multimap::erase

unordered_multimap::swap

unordered_multimap::extract (C++17)

unordered_multimap::merge (C++17)

Lookup

unordered_multimap::count

unordered_multimap::find

unordered_multimap::contains (C++20)

unordered_multimap::equal_range

Bucket interface

unordered_multimap::begin(size_type)unordered_multimap::cbegin(size_type)

unordered_multimap::end(size_type)unordered_multimap::cend(size_type)

unordered_multimap::bucket_count

unordered_multimap::max_bucket_count

unordered_multimap::bucket_size

unordered_multimap::bucket

Hash policy

unordered_multimap::load_factor

unordered_multimap::max_load_factor

unordered_multimap::rehash

unordered_multimap::reserve

Observers

unordered_multimap::hash_function

unordered_multimap::key_eq

Deduction guides(C++17)

 

bool contains( const Key& key ) const;	(1)	(since C++20)
bool contains( const Key& key, std::size_t hash ) const;	(1)	(since C++20)
template< class K > bool contains( const K& x ) const;	(2)	(since C++20)
template< class K > bool contains( const K& x, std::size_t hash ) 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 only participates in overload resolution if the qualified-id Hash::transparent_key_equal is valid and denotes a type. This assumes that such Hash is callable with both K and Key type, and that its key_equal is transparent, which, together, allows calling this function without constructing an instance of Key.

If present, the hash parameter may be used to pass a pre-computed hash value as an optimization. The behavior is undefined if invoking hash_function() on the key passed do not produce the same value as hash.

Parameters

key	-	key value of the element to search for
x	-	a value of any type that can be transparently compared with a key
hash	-	the hash value of the 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_map>
 
int main()
{
    std::unordered_multimap<int,char> example = {{1,'a'},{2,'b'}};
 
    if(example.contains(2)) {
        std::cout << "Found\n";
    } else {
        std::cout << "Not found\n";
    }
}

Output:

Found

See also

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