std::erase() method

od C++20

// prism-push-types:size_type
// (1)
template< class T, class Alloc, class U >
constexpr typename std::vector<T,Alloc>::size_type
    erase( std::vector<T,Alloc>& c, U const& value )

// (2) 
template< class T, class Alloc, class Pred >
constexpr typename std::vector<T,Alloc>::size_type
    erase_if( std::vector<T,Alloc>& c, Pred pred );

• (1) Erases all elements that compare equal to value from the container. Equivalent to

  auto it = std::remove(c.begin(), c.end(), value);
  auto r = std::distance(it, c.end());
  c.erase(it, c.end());
  return r;
• (2) Erases all elements that satisfy the predicate pred from the container. Equivalent to

  auto it = std::remove_if(c.begin(), c.end(), pred);
  auto r = std::distance(it, c.end());
  c.erase(it, c.end());
  return r;

Parameters

• c - container from which to erase
• value - value to be removed the value to initialize the new elements with
• pred - unary predicate which returns true if the element should be erased The expression pred(v) must be convertible to bool for every argument v of type (possibly const) T, regardless of value category, and must not modify v. Thus, a parameter type of T& is not allowed (nor is T unless for T a move is equivalent to a copy (since C++11)).

Return value

The number of erased elements.

Complexity

Linear.

Exceptions

(none)

Example

Main.cpp

#include <iostream>
#include <numeric>
#include <string_view>
#include <vector>
 
void print_container(std::string_view comment, const std::vector<char>& c)
{
    std::cout << comment;
    for (auto x : c) {
        std::cout << x << ' ';
    }
    std::cout << '\n';
}
 
int main()
{
    std::vector<char> cnt(10);
    std::iota(cnt.begin(), cnt.end(), '0');
    print_container("Init:\n", cnt);
 
    std::erase(cnt, '3');
    print_container("Erase '3':\n", cnt);
 
    auto erased = std::erase_if(cnt, [](char x) { return (x - '0') % 2 == 0; });
    print_container("Erase all even numbers:\n", cnt);
    std::cout << erased << " even numbers were erased.\n";
}

Output

Init:
0 1 2 3 4 5 6 7 8 9 
Erase '3':
0 1 2 4 5 6 7 8 9 
Erase all even numbers:
1 5 7 9
5 even numbers were erased.