std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::equal_range

 

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std::unordered_multiset

Member types
Member functions
unordered_multiset::unordered_multiset unordered_multiset::~unordered_multiset    unordered_multiset::operator= unordered_multiset::get_allocator Iterators unordered_multiset::beginunordered_multiset::cbegin unordered_multiset::endunordered_multiset::cend Capacity unordered_multiset::size unordered_multiset::max_size unordered_multiset::empty Modifiers unordered_multiset::clear unordered_multiset::insert unordered_multiset::insert_range (C++23) unordered_multiset::emplace unordered_multiset::emplace_hint unordered_multiset::erase unordered_multiset::swap unordered_multiset::extract (C++17) unordered_multiset::merge (C++17)	Lookup unordered_multiset::count unordered_multiset::find unordered_multiset::contains (C++20) unordered_multiset::equal_range Bucket interface unordered_multiset::begin(size_type)unordered_multiset::cbegin(size_type) unordered_multiset::end(size_type)unordered_multiset::cend(size_type) unordered_multiset::bucket_count unordered_multiset::max_bucket_count unordered_multiset::bucket_size unordered_multiset::bucket Hash policy unordered_multiset::load_factor unordered_multiset::max_load_factor unordered_multiset::rehash unordered_multiset::reserve Observers unordered_multiset::hash_function unordered_multiset::key_eq
Non-member functions
operator==operator!= (until C++20)	std::swap(std::unordered_multiset) erase_if(std::unordered_multiset) (C++20)
Deduction guides (C++17)

 

std::pair<iterator, iterator> equal_range( const Key& key );	(1)	(since C++11)
std::pair<const_iterator, const_iterator> equal_range( const Key& key ) const;	(2)	(since C++11)
template< class K > std::pair<iterator, iterator> equal_range( const K& x );	(3)	(since C++20)
template< class K > std::pair<const_iterator, const_iterator> equal_range( const K& x ) const;	(4)	(since C++20)

1,2) Returns a range containing all elements with key key in the container. The range is defined by two iterators, the first pointing to the first element of the wanted range and the second pointing past the last element of the range.

3,4) Returns a range containing all elements in the container with key equivalent to 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 to compare the elements to
x	-	a value of any type that can be transparently compared with a key

Return value

std::pair containing a pair of iterators defining the wanted range. If there are no such elements, past-the-end (see end()) iterators are returned as both elements of the pair.

Complexity

Average case linear in the number of elements with the key key, worst case linear in the size of the container.

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_generic_unordered_lookup	201811L	(C++20)	Heterogeneous comparison lookup in unordered associative containers, overloads (3,4)

Example

Estimates the characters frequency for given string.

Run this code

#include <iostream>
#include <iterator>
#include <string>
#include <unordered_set>
 
int main()
{
    std::string sentence{"cppreference.com"};
    std::cout << "The sentence: " << sentence << '\n';
 
    std::unordered_multiset<char> sequence;
    for (char x : sentence)
        sequence.insert(x);
 
    std::cout << "The sequence: { ";
    for (char x : sequence)
        std::cout << x << ' ';
 
    std::cout << "}\n" "Symbol:Frequency: ";
    for (auto it = sequence.begin(); it != sequence.end();)
    {
        if (auto [first, last] = sequence.equal_range(*it); first != last)
        {
            std::cout << *first << ":" << std::distance(first, last) << "  ";
            it = last;
        }
        else
            ++it;
    }
}

Possible output:

The sentence: cppreference.com
The sequence: { m o c c c p p r r e e e e f n . }
Symbol:Frequency: m:1  o:1  c:3  p:2  r:2  e:4  f:1  n:1  .:1

See also

find	finds element with specific key (public member function)
contains (C++20)	checks if the container contains 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 (function template)