std::multiset erase() method

od C++23

// (1) Non const version only
iterator erase( iterator pos );
iterator erase( const_iterator pos );

// (2) Non const version only
iterator erase( iterator first, iterator last );

// (3) Non const version only
size_type erase( const Key& key );

// (4) Non const version only
template< class K >
size_type erase( K&& x );

od C++11

// (1) Non const version only
iterator erase( iterator pos );
iterator erase( const_iterator pos );

// (2) Non const version only
iterator erase( iterator first, iterator last );

// (3) Non const version only
size_type erase( const Key& key );

do C++11

// (1) Non const version only
void erase( iterator pos );

// (2) Non const version only
void erase( iterator first, iterator last );

// (3) Non const version only
size_type erase( const Key& key );

Removes specified elements from the container.

• (1) Removes the element at pos.
  od C++11

  Only one overload is provided if iterator and const_iterator are the same type.
• (2) Removes the elements in the range [ first; last ), which must be a valid range in *this.
• (3) Removes the element with the key equivalent to key.
• (4) Removes the element 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.

Invalidation

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

important

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

• (1-2)
  od C++11

  Iterator following the last removed element.

  do C++11

  (none)
• (3,4) Number of elements removed.

Exceptions

• (1,2) Throws nothing.
• (3,4) Any exceptions thrown by the Compare object.

Complexity

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

Notes

Feature testing macro: __cpp_lib_associative_heterogeneous_erasure (for overload (4)).

Example

Main.cpp

#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();
}

Output

c = { 1 1 2 2 3 3 4 4 }
Erase all odd numbers:
c = { 2 2 4 4 }
Erase 1, erased count: 0
Erase 2, erased count: 2
Erase 2, erased count: 0
c = { 4 4 }