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

	(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 $\scriptsize N$ $N$ 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 <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

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

Sequence
array (C++11)
vector
vector<bool>
inplace_vector (C++26)
deque
forward_list (C++11)
list
Associative
set
multiset
map
multimap
Unordered associative
unordered_set (C++11)
unordered_multiset (C++11)
unordered_map (C++11)
unordered_multimap (C++11)
Adaptors
stack
queue
priority_queue
flat_set (C++23)
flat_multiset (C++23)
flat_map (C++23)
flat_multimap (C++23)
Views
span (C++20)
mdspan (C++23)
Tables
Iterator invalidation
Member function table
Non-member function table