std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::equal_range
From cppreference.com
< cpp | container | unordered map
|
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
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()
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
Run this code
#include <iostream> #include <unordered_map> int main() { std::unordered_map<int,char> map = {{1, 'a'},{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 a
See also
| finds element with specific key (public member function) |
|
|
(C++20)
|
checks if the container contains element with specific key (public member function) |
| returns the number of elements matching specific key (public member function) |
|
| returns range of elements matching a specific key (function template) |