std::forward_list<T,Allocator>::forward_list
From cppreference.com
< cpp | container | forward list
| forward_list() : forward_list(Allocator()) {} |
(1) | |
| explicit forward_list( const Allocator& alloc ); |
(2) | |
| explicit forward_list( size_type count, const Allocator& alloc = Allocator() ); |
(3) | |
| forward_list( size_type count, const T& value, const Allocator& alloc = Allocator() ); |
(4) | |
| template< class InputIt > forward_list( InputIt first, InputIt last, |
(5) | |
| template< container-compatible-range<T> R > forward_list( std::from_range_t, R&& rg, |
(6) | (since C++23) |
| forward_list( const forward_list& other ); |
(7) | |
| forward_list( forward_list&& other ); |
(8) | |
| (9) | ||
| forward_list( const forward_list& other, const Allocator& alloc ); |
(until C++23) | |
| forward_list( const forward_list& other, const std::type_identity_t<Allocator>& alloc ); |
(since C++23) | |
| (10) | ||
| forward_list( forward_list&& other, const Allocator& alloc ); |
(until C++23) | |
| forward_list( forward_list&& other, const std::type_identity_t<Allocator>& alloc ); |
(since C++23) | |
| forward_list( std::initializer_list<T> init, const Allocator& alloc = Allocator() ); |
(11) | |
Constructs a new forward_list from a variety of data sources, optionally using a user supplied allocator alloc.
1) The default constructor. Constructs an empty
forward_list with a default-constructed allocator. If
Allocator is not DefaultConstructible, the behavior is undefined.2) Constructs an empty
forward_list with the given allocator alloc.3) Constructs a
forward_list with count default-inserted objects of T. No copies are made.4) Constructs a
forward_list with count copies of elements with value value.5) Constructs a
forward_list with the contents of the range [first, last). Each iterator in [first, last) is dereferenced exactly once. This overload participates in overload resolution only if
InputIt satisfies the requirements of LegacyInputIterator.6) Constructs a
forward_list with the contents of the range rg. Each iterator in rg is dereferenced exactly once. If
T is not EmplaceConstructible into std::forward_list<T> from *ranges::begin(rg), the behavior is undefined.7-10) Constructs a
forward_list with the contents of other.7) The copy constructor. The allocator is obtained as if by calling std::allocator_traits<Allocator>::
select_on_container_copy_construction
(other.get_allocator()).
select_on_container_copy_construction
(other.get_allocator()).
8) The move constructor. The allocator is obtained by move construction from other.get_allocator().
9) Same as the copy constructor, except that alloc is used as the allocator.
10) Same as the move constructor, except that alloc is used as the allocator.
11) Equivalent to forward_list(il.begin(), il.end(), alloc).
Contents |
[edit] Parameters
| alloc | - | allocator to use for all memory allocations of this container |
| count | - | the size of the container |
| value | - | the value to initialize elements of the container with |
| first, last | - | the range to copy the elements from |
| other | - | another container to be used as source to initialize the elements of the container with |
| init | - | initializer list to initialize the elements of the container with |
| rg | - | a container compatible range |
[edit] Complexity
1,2) Constant.
3,4) Linear in count.
5) Linear in std::distance(first, last).
6) Linear in ranges::distance(rg).
7) Linear in other.size().
8) Constant.
9) Linear in other.size().
10) Linear in other.size() if alloc != other.get_allocator(), otherwise constant.
11) Linear in init.size().
[edit] Exceptions
Calls to Allocator::allocate may throw.
[edit] Notes
After container move construction (overload (8)), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.reqmts]/67, and a more direct guarantee is under consideration via LWG issue 2321.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_containers_ranges |
202202L | (C++23) | Ranges-aware construction and insertion; overload (6) |
[edit] Example
Run this code
#include <forward_list> #include <iostream> #include <string> template<typename T> std::ostream& operator<<(std::ostream& s, const std::forward_list<T>& v) { s.put('{'); for (char comma[]{'\0', ' ', '\0'}; const auto& e : v) s << comma << e, comma[0] = ','; return s << "}\n"; } int main() { // C++11 initializer list syntax: std::forward_list<std::string> words1{"the", "frogurt", "is", "also", "cursed"}; std::cout << "1: " << words1; // words2 == words1 std::forward_list<std::string> words2(words1.begin(), words1.end()); std::cout << "2: " << words2; // words3 == words1 std::forward_list<std::string> words3(words1); std::cout << "3: " << words3; // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"} std::forward_list<std::string> words4(5, "Mo"); std::cout << "4: " << words4; const auto rg = {"cat", "cow", "crow"}; #ifdef __cpp_lib_containers_ranges std::forward_list<std::string> words5(std::from_range, rg); // overload (6) #else std::forward_list<std::string> words5(rg.begin(), rg.end()); // overload (5) #endif std::cout << "5: " << words5; }
Output:
1: {the, frogurt, is, also, cursed}
2: {the, frogurt, is, also, cursed}
3: {the, frogurt, is, also, cursed}
4: {Mo, Mo, Mo, Mo, Mo}
5: {cat, cow, crow}[edit] 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 2193 | C++11 | the default constructor was explicit | made non-explicit |
| LWG 2210 | C++11 | overload (3) did not have an allocator parameter | added the parameter |
| N3346 | C++11 | for overload (3), the elements in the container were value-initialized |
they are default-inserted |
[edit] See also
| assigns values to the container (public member function) | |
| assigns values to the container (public member function) |
