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

From cppreference.com

 
C++
 
Containers library
 
std::forward_list
Member functions
(C++23)
Element access
Iterators
Capacity
Modifiers
(C++23)
(C++23)
Operations
forward_list::removeforward_list::remove_if
Non-member functions
(C++20)(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Deduction guides(C++17)
 
(1)
void remove( const T& value );
 (since C++11)
(until C++20)
size_type remove( const T& value );
 (since C++20)
(2)
template< class UnaryPredicate >
void remove_if( UnaryPredicate p );
 (since C++11)
(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 Comment
__cpp_lib_list_remove_return_type 201806L (C++20) Change the return type

Example

Run this code
#include <forward_list>
#include <iostream>
 
int main()
{
    std::forward_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

See also

 removes elements satisfying specific criteria
(function template)
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