std::unordered_set<Key,Hash,KeyEqual,Allocator>::erase

Since C++23

Removes specified elements from the container. The order of the remaining elements is preserved. (This makes it possible to erase individual elements while iterating through the container.)

# Declarations

iterator erase( iterator pos );

(since C++11) (until C++23)

iterator erase( iterator pos )
requires(!std::same_as<iterator, const_iterator>);

(since C++23)

iterator erase( const_iterator pos );

(since C++11)

iterator erase( const_iterator first, const_iterator last );

(since C++11)

size_type erase( const Key& key );

(since C++11)

template< class K >
size_type erase( K&& x );

(since C++23)

# Parameters

pos: iterator to the element to remove
first, last: range of elements to remove
key: key value of the elements to remove
x: a value of any type that can be transparently compared with a key denoting the elements to remove

# Notes

Feature-test macro Value Std Feature __cpp_lib_associative_heterogeneous_erasure 202110L (C++23) Heterogeneous erasure in associative containers and unordered associative containers; overload (5)

# Example

#include <unordered_set>
#include <iostream>
 
int main()
{
    std::unordered_set<int> c = {1, 2, 3, 4, 1, 2, 3, 4};
 
    auto print = [&c]
    {
        std::cout << "c = { ";
        for (int n : c)
            std::cout << n << ' ';
        std::cout << "}\n";
    };
    print();
 
    std::cout << "Erase all odd numbers:\n";
    for (auto it = c.begin(); it != c.end();)
    {
        if (*it % 2 != 0)
            it = c.erase(it);
        else
            ++it;
    }
    print();
 
    std::cout << "Erase 1, erased count: " << c.erase(1) << '\n';
    std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
    std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
    print();
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 2059	C++11	there was ambiguity for overload (2)	added overload (1)
LWG 2356	C++11	the order of non-equivalent elements that arenot erased was not guaranteed to be preserved	required to be preserved

# See also

clear