std::flat_multiset<Key,Compare,KeyContainer>:: erase

From cppreference.com

iterator erase ( iterator position ) ;
(1) (since C++23)
iterator erase ( const_iterator pos ) ;
(2) (since C++23)
iterator erase ( const_iterator first, const_iterator last ) ;
(3) (since C++23)
size_type erase ( const Key & key ) ;
(4) (since C++23)
template < class K >
size_type erase ( K && x ) ;
(5) (since C++23)

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

1,2) Removes the element at pos .
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 .

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

Depends on underlying container. Typically linear.

Example

#include <flat_set>
#include <iostream>
 
int main()
{
    std::flat_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();
}

See also

clears the contents
(public member function)