std::set 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( const_iterator first, const_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( const_iterator first, const_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 );

• (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 (if one exists) with the key equivalent to key.
• (4) Removes the element (if one exists) 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 - O(size()). 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 iterators and references are not invalidated.

Valid iterator

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid - O(size()).

Parameters

• pos - iterator to the element to remove
• first - O(size()).
• 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) - Iterator following the last removed element.
• (3-4) - Number of elements removed (0 or 1).

Complexity

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

Exceptions

• (1-2) (none)
• (3-4) Any exceptions thrown by the Hash and KeyEqual object.

Notes

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

Example

Main.cpp

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

Possible output

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