std::list<T,Allocator>::remove, remove_if

	(1)
void remove( const T& value );		(until C++20)
size_type remove( const T& value );		(since C++20)
	(2)
template< class UnaryPredicate > void remove_if( UnaryPredicate p );		(until C++20)
template< class UnaryPredicate > size_type remove_if( UnaryPredicate p );		(since C++20)

Removes all elements satisfying specific criteria. Invalidates only the iterators and references to the removed elements.

1) Removes all elements that are equal to value (using operator==).

2) Removes all elements for which predicate p returns true.

Parameters

value	-	value of the elements to remove
p	-	unary predicate which returns `true` if the element should be removed. The expression `p(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).
Type requirements
-`UnaryPredicate` must meet the requirements of Predicate.

Return value

(none)	(until C++20)
The number of elements removed.	(since C++20)

Complexity

Given \(\scriptsize N\)N as std::distance(begin(), end()):

1) Exactly \(\scriptsize N\)N comparisons using operator==.

2) Exactly \(\scriptsize N\)N applications of the predicate p.

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_list_remove_return_type`	201806L	(C++20)	Change the return type

Example

#include <list>
#include <iostream>
 
int main()
{
    std::list<int> l = {1, 100, 2, 3, 10, 1, 11, -1, 12};
 
    auto count1 = l.remove(1);
    std::cout << count1 << " elements equal to 1 were removed\n";
 
    auto count2 = l.remove_if([](int n){ return n > 10; });
    std::cout << count2 << " elements greater than 10 were removed\n";
 
    std::cout << "Finally, the list contains: ";
    for (int n : l)
        std::cout << n << ' ';
    std::cout << '\n';
}

Output:

2 elements equal to 1 were removed
3 elements greater than 10 were removed
Finally, the list contains: 2 3 10 -1

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 1207	C++98	it was unclear whether iterators and/or references will be invalidated	only invalidates iterators and references to the removed elements