std::unordered_map::erase

iterator erase( const_iterator pos );	(1)	(since C++11)
iterator erase( const_iterator first, const_iterator last );	(2)	(since C++11)
size_type erase( const key_type& key );	(3)	(since C++11)

Removes specified elements from the container.

1) Removes the element at pos.

2) Removes the elements in the range [first; last), which must be a valid range in *this.

3) Removes the element (if one exists) with the key equivalent to key.

References and iterators to the erased elements are invalidated. Other iterators and references are not invalidated.

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferencable) cannot be used as a value for pos.

The order of the elements that are not erased is preserved (this makes it possible to erase individual elements while iterating through the container)

(since C++14)

Parameters

pos	-	iterator to the element to remove
first, last	-	range of elements to remove
key	-	key value of the elements to remove

Return value

1-2) Iterator following the last removed element.

3) Number of elements removed.

Exceptions

1,2) (none)

3) Any exceptions thrown by the Compare object.

Complexity

Given an instance c of unordered_map:

1) Average case: constant, worst case: c.size()

2) Average case: std::distance(first, last), worst case: c.size()

3) Average case: c.count(key), worst case: c.size()

Example

Run this code

#include <unordered_map>
#include <iostream>
int main()
{
    std::unordered_map<int, std::string> c = {{1, "one"}, {2, "two"}, {3, "three"},
                                    {4, "four"}, {5, "five"}, {6, "six"}};
    // erase all odd numbers from c
    for(auto it = c.begin(); it != c.end(); )
        if(it->first % 2 == 1)
            it = c.erase(it);
        else
            ++it;
    for(auto& p : c)
        std::cout << p.second << ' ';
}

Possible output:

two four six

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators 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

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