std::erase, std::erase_if (std::forward_list)

Containers library
Unordered associative
Defined in header <forward_list>
template< class T, class Alloc, class U >

typename std::forward_list<T,Alloc>::size_type

    erase(std::forward_list<T,Alloc>& c, const U& value);
(1) (since C++20)
template< class T, class Alloc, class Pred >

typename std::forward_list<T,Alloc>::size_type

    erase_if(std::forward_list<T,Alloc>& c, Pred pred);
(2) (since C++20)
1) Erases all elements that compare equal to value from the container. Equivalent to return c.remove_if([&](auto& elem) { return elem == value; });
2) Erases all elements that satisfy the predicate pred from the container. Equivalent to return c.remove_if(pred);


[edit] Parameters

c - container from which to erase
value - value to be removed
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). ​

[edit] Return value

The number of erased elements.

[edit] Complexity



Unlike std::forward_list::remove, erase accepts heterogenous types and does not force a conversion to the container's value type before invoking the == operator.

[edit] Example

#include <iostream>
#include <numeric>
#include <string_view>
#include <forward_list>
void print_container(std::string_view comment, const std::forward_list<char>& c)
    std::cout << comment;
    for (auto x : c) {
        std::cout << x << ' ';
    std::cout << '\n';
int main()
    std::forward_list<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 << "In all " << erased << " even numbers were erased.\n";


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
In all 5 even numbers were erased.

[edit] See also

removes elements satisfying specific criteria
(function template) [edit]
removes elements satisfying specific criteria
(public member function) [edit]