NAME

std::multiset::erase - std::multiset::erase

Synopsis

iterator erase( iterator pos ); (until C++23)
iterator erase( iterator pos )
requires(!std::same_as<iterator, (since C++23)
const_iterator>);
iterator erase( const_iterator pos ); (2) (since C++11)
iterator erase( iterator first, iterator last ); (1) (until C++11)
iterator erase( const_iterator first, (since C++11)
const_iterator last ); (3)
size_type erase( const Key& key ); (4)
template< class K > (5) (since C++23)
size_type erase( K&& x );

Removes specified elements from the container. The order of the remaining equivalent
elements is preserved.

1,2) Removes the element at pos.
Only one overload is provided if iterator and const_iterator are the same type.
(since C++11)
3) Removes the elements in the range [first, last), which must be a valid range in
*this.
4) Removes all elements with the key equivalent to key.
5) Removes all elements with key that compares equivalent to the value x. This
overload participates in overload resolution only if the qualified-id
Compare::is_transparent is valid and denotes a type, and neither iterator nor
const_iterator is implicitly convertible from K. It allows calling this function
without constructing an instance of Key.

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

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

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

Return value

1-3) Iterator following the last removed element.
4) Number of elements removed.
5) Number of elements removed.

Exceptions

1-3) Throws nothing.
4,5) Any exceptions thrown by the Compare object.

Complexity

Given an instance c of multiset:

1,2) Amortized constant
3) log(c.size()) + std::distance(first, last)
4) log(c.size()) + c.count(key)
5) log(c.size()) + c.count(x)

Notes

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

Example

// Run this code

#include <set>
#include <iostream>

int main()
{
std::multiset<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

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
the return type of overloads (1) and (3)
LWG 130 C++98 was void (it is not corrected to iterator
consistent with the erase() requirement
on sequence containers)
the order of equivalent elements that
LWG 371 C++98 are not required to be
erased was not guaranteed to be preserved
preserved
LWG 2059 C++11 replacing overload (1) with overload (2) added overload (1) back
introduced new ambiguity