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

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std::unordered_multimap

Member types

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unordered_multimap::unordered_multimap
unordered_multimap::~unordered_multimap
unordered_multimap::operator=
unordered_multimap::get_allocator
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unordered_multimap::beginunordered_multimap::cbegin
unordered_multimap::endunordered_multimap::cend
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Lookup
unordered_multimap::count
unordered_multimap::find
unordered_multimap::contains (C++20)
unordered_multimap::equal_range
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unordered_multimap::begin(size_type)unordered_multimap::cbegin(size_type)
unordered_multimap::end(size_type)unordered_multimap::cend(size_type)
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unordered_multimap::key_eq

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std::swap(std::unordered_multimap)
erase_if(std::unordered_multimap) (C++20)

operator==operator!=

(until C++20)

Deduction guides(C++17)

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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 keykey 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 tox. This overload participates in overload resolution only ifHash andKeyEqual are bothtransparent. This assumes that suchHash is callable with bothK andKey type, and that theKeyEqual is transparent, which, together, allows calling this function without constructing an instance ofKey.

[edit]Parameters

key	-	key value to compare the elements to
x	-	a value of any type that can be transparently compared with a key

[edit]Return value

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

[edit]Complexity

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

[edit]Notes

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

[edit]Example

Run this code

#include <iostream>#include <unordered_map> int main(){std::unordered_multimap<int,char> map={{1,'a'},{1,'b'},{1,'d'},{2,'b'}};auto range= map.equal_range(1);for(auto it= range.first; it!= range.second;++it)std::cout<< it->first<<' '<< it->second<<'\n';}

Output:

1 a1 b1 d

[edit]See also

find	finds element with specific key (public member function)[edit]
contains (C++20)	checks if the container contains element with specific key (public member function)[edit]
count	returns the number of elements matching specific key (public member function)[edit]
equal_range	returns range of elements matching a specific key (function template)[edit]