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

 

C++

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Technical specifications

Symbols index

External libraries

 

Containers library

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array (C++11)

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forward_list (C++11)

list

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std::forward_list

Member functions

forward_list::forward_list

forward_list::~forward_list

forward_list::operator=

forward_list::assign

forward_list::get_allocator

Element access

forward_list::front

Iterators

forward_list::before_beginforward_list::cbefore_begin

forward_list::beginforward_list::cbegin

forward_list::endforward_list::cend

Capacity

forward_list::empty

forward_list::max_size

Modifiers

forward_list::clear

forward_list::insert_after

forward_list::emplace_after

forward_list::erase_after

forward_list::push_front

forward_list::emplace_front

forward_list::pop_front

forward_list::resize

forward_list::swap

Operations

forward_list::merge

forward_list::splice_after

forward_list::removeforward_list::remove_if

forward_list::reverse

forward_list::unique

forward_list::sort

Non-member functions

std::swap

eraseerase_if (C++20)(C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Deduction guides(C++17)

 

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

Run this code

#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

removeremove_if	removes elements satisfying specific criteria (function template)
removeremove_if (C++11)	removes elements satisfying specific criteria (public member function)