std::forward_list - cppreference.com (original) (raw)

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, std::forward_list objects generally cannot be constexpr, because any dynamically allocated storage must be released in the same evaluation of constant expression. (since C++26)

Contents

[edit] Template parameters

T - 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. Feature-test macro Value Std Feature __cpp_lib_incomplete_container_elements 201505L (C++17) Minimal incomplete type support (since C++17) [edit]
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.[edit]

[edit] Member types

Member type Definition
value_type T[edit]
allocator_type Allocator[edit]
size_type Unsigned integer type (usually std::size_t)[edit]
difference_type Signed integer type (usually std::ptrdiff_t)[edit]
reference value_type&[edit]
const_reference const value_type&[edit]
pointer std::allocator_traits<Allocator>::pointer[edit]
const_pointer std::allocator_traits<Allocator>::const_pointer[edit]
iterator LegacyForwardIterator and ConstexprIterator(since C++26) to value_type[edit]
const_iterator LegacyForwardIterator and ConstexprIterator(since C++26) to const value_type[edit]

[edit] Member functions

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

[edit] Non-member functions

[edit] Notes

Feature-test macro Value Std Feature
__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

[edit] Example

[edit] See also