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

From cppreference.com

 
 
Containers library
Sequence
(C++11)
Associative
Unordered associative
Adaptors
Views
(C++20)
 
 
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);

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). ​

Return value

The number of erased elements.

Complexity

Linear.

Notes

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.

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("Initially, cnt = ", cnt);
 
    std::erase(cnt, '3');
    print_container("After erase '3', cnt = ", cnt);
 
    auto erased = std::erase_if(cnt, [](char x) { return (x - '0') % 2 == 0; });
    print_container("After erase all even numbers, cnt = ", cnt);
    std::cout << "Erased even numbers: " << erased << '\n';
}

Output:

Initially, cnt = { 0 1 2 3 4 5 6 7 8 9 }
After erase '3', cnt = { 0 1 2 4 5 6 7 8 9 }
After erase all even numbers, cnt = { 1 5 7 9 }
Erased even numbers: 5

See also

removes elements satisfying specific criteria
(function template)
removes elements satisfying specific criteria
(public member function)