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

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C++
Containers library
std::list
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
(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 N as std:: distance ( begin ( ) , end ( ) ) :

1) Exactly N comparisons using operator == .
2) Exactly 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

Run this code 
#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

See also

removes elements satisfying specific criteria
(function template)
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