std::forward_list

Defined in header `<forward_list>`
template< class T, class Allocator = std::allocator<T> > class forward_list;	(1)	(since C++11)
namespace pmr { template< class T > using forward_list = std::forward_list<T, std::pmr::polymorphic_allocator<T>>; }	(2)	(since C++17)

std::forward_list is a container that supports fast insertion and removal of elements from anywhere in the container. Fast random access is not supported. It is implemented as a singly-linked list. Compared to std::list this container provides more space efficient storage when bidirectional iteration is not needed.

Adding, removing and moving the elements within the list, or across several lists, does not invalidate the iterators currently referring to other elements in the list. However, an iterator or reference referring to an element is invalidated when the corresponding element is removed (via erase_after) from the list.

std::forward_list meets the requirements of Container (except for the size member function and that operator=='s complexity is always linear), AllocatorAwareContainer and SequenceContainer.

All member functions of std::forward_list are constexpr: it is possible to create and use std::forward_list objects in the evaluation of a constant expression.

However, defining a constexpr std::forward_list variable is generally an error, because constant evaluation requires any dynamically allocated storage to be released in the same evaluation, which is usually not the case with std::forward_list's initializer.

(since C++26)

Template parameters

The type of the elements.

The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type is a complete type and meets the requirements of Erasable, but many member functions impose stricter requirements.

(until C++17)

The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type meets the requirements of Erasable, but many member functions impose stricter requirements. This container (but not its members) can be instantiated with an incomplete element type if the allocator satisfies the allocator completeness requirements.

(since C++17)

Allocator - An allocator that is used to acquire/release memory and to construct/destroy the elements in that memory. The type must meet the requirements of Allocator. The behavior is undefined(until C++20)The program is ill-formed(since C++20) if Allocator::value_type is not the same as T.

Member types

Member type	Definition
`value_type`	`T`
`allocator_type`	`Allocator`
`size_type`	unsigned integer type (usually `std::size_t`)
`difference_type`	signed integer type (usually `std::ptrdiff_t`)
`reference`	value_type&
`const_reference`	constvalue_type&
`pointer`	std::allocator_traits<Allocator>::pointer
`const_pointer`	std::allocator_traits<Allocator>::const_pointer
`iterator`	LegacyForwardIterator and ConstexprIterator(since C++26) to `value_type`
`const_iterator`	LegacyForwardIterator and ConstexprIterator(since C++26) to constvalue_type

Member functions

(constructor)	constructs the `forward_list` (public member function)
(destructor)	destructs the `forward_list` (public member function)
operator=	assigns values to the container (public member function)
assign	assigns values to the container (public member function)
assign_range (C++23)	assigns a range of values to the container (public member function)
get_allocator	returns the associated allocator (public member function)
Element access
front	access the first element (public member function)
Iterators
before_begincbefore_begin	returns an iterator to the element before beginning (public member function)
begincbegin	returns an iterator to the beginning (public member function)
endcend	returns an iterator to the end (public member function)
Capacity
empty	checks whether the container is empty (public member function)
max_size	returns the maximum possible number of elements (public member function)
Modifiers
clear	clears the contents (public member function)
insert_after	inserts elements after an element (public member function)
emplace_after	constructs elements in-place after an element (public member function)
insert_range_after (C++23)	inserts a range of elements after an element (public member function)
erase_after	erases an element after an element (public member function)
push_front	inserts an element to the beginning (public member function)
emplace_front	constructs an element in-place at the beginning (public member function)
prepend_range (C++23)	adds a range of elements to the beginning (public member function)
pop_front	removes the first element (public member function)
resize	changes the number of elements stored (public member function)
swap	swaps the contents (public member function)
Operations
merge	merges two sorted lists (public member function)
splice_after	moves elements from another `forward_list` (public member function)
removeremove_if	removes elements satisfying specific criteria (public member function)
reverse	reverses the order of the elements (public member function)
unique	removes consecutive duplicate elements (public member function)
sort	sorts the elements (public member function)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++11)(C++11)(removed in C++20)(C++11)(removed in C++20)(C++11)(removed in C++20)(C++11)(removed in C++20)(C++11)(removed in C++20)(C++20)	lexicographically compares the values of two `forward_list`s (function template)
std::swap(std::forward_list) (C++11)	specializes the `std::swap` algorithm (function template)
erase(std::forward_list)erase_if(std::forward_list) (C++20)	erases all elements satisfying specific criteria (function template)

Deduction guides

(since C++17)

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_incomplete_container_elements`	`201505L`	(C++17)	Minimal incomplete type support
`__cpp_lib_containers_ranges`	`202202L`	(C++23)	Ranges construction and insertion for containers
`__cpp_lib_constexpr_forward_list`	`202502L`	(C++26)	Constexpr `std::forward_list`

std::forward_list

Template parameters

Member types

Member functions

Element access

Iterators

Capacity

Modifiers

Operations

Non-member functions

Deduction guides

Notes

Example

See also