NAME¶

std::erase,std::erase_if(std::list) - std::erase,std::erase_if(std::list)

Synopsis¶

Defined in header <list>
template< class T, class Alloc, class U >
(since C++20)
std::list<T, Alloc>::size_type (until C++26)

erase( std::list<T, Alloc>& c, const U& value );
template< class T, class Alloc, class U = T >

std::list<T, Alloc>::size_type (1) (since C++26)

erase( std::list<T, Alloc>& c, const U& value );
template< class T, class Alloc, class Pred >

std::list<T, Alloc>::size_type (2) (since C++20)

erase_if( std::list<T, Alloc>& c, Pred pred );

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
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
pred - 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::list::remove, erase accepts heterogeneous types and does not force a
conversion to the container's value type before invoking the == operator.

Feature-test macro Value Std Feature
__cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for
algorithm (1)

Example¶

// Run this code

#include <complex>
#include <iostream>
#include <numeric>
#include <string_view>
#include <list>

void println(std::string_view comment, const auto& c)
{
std::cout << comment << "{ ";
for (const auto& x : c)
std::cout << x << ' ';
std::cout << "}\n";
}

int main()
{
std::list<char> cnt(10);
std::iota(cnt.begin(), cnt.end(), '0');
println("Initially, cnt = ", cnt);

std::erase(cnt, '3');
println("After erase '3', cnt = ", cnt);

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

std::list<std::complex<double>> nums{{2, 2}, {4, 2}, {4, 8}, {4, 2}};
#ifdef __cpp_lib_algorithm_default_value_type
std::erase(nums, {4, 2});
#else
std::erase(nums, std::complex<double>{4, 2});
#endif
println("After erase {4, 2}, nums = ", nums);
}

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
After erase {4, 2}, nums = { (2,2) (4,8) }

See also¶

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