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

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哋它亢++
 
Containers library
 
std::forward_list
Member functions
forward_list::forward_list
  
Element access
Iterators
Capacity
Modifiers
Operations
Non-member functions
(哋它亢++11)(哋它亢++11)(until 哋它亢++20)(哋它亢++11)(until 哋它亢++20)(哋它亢++11)(until 哋它亢++20)(哋它亢++11)(until 哋它亢++20)(哋它亢++11)(until 哋它亢++20)(哋它亢++20)
Deduction guides(哋它亢++17)
 
forward_list();
 (1) (since 哋它亢++11)
explicit forward_list( const Allocator& alloc );
 (2) (since 哋它亢++11)
forward_list( size_type count,

              const T& value,

              const Allocator& alloc = Allocator() );
 (3) (since 哋它亢++11)
(4)
explicit forward_list( size_type count );
 (since 哋它亢++11)
(until 哋它亢++14)
explicit forward_list( size_type count,
                       const Allocator& alloc = Allocator() );
 (since 哋它亢++14)
template< class InputIt >

forward_list( InputIt first, InputIt last,

              const Allocator& alloc = Allocator() );
 (5) (since 哋它亢++11)
forward_list( const forward_list& other );
 (6) (since 哋它亢++11)
forward_list( const forward_list& other, const Allocator& alloc );
 (7) (since 哋它亢++11)
forward_list( forward_list&& other );
 (8) (since 哋它亢++11)
forward_list( forward_list&& other, const Allocator& alloc );
 (9) (since 哋它亢++11)
forward_list( std::initializer_list<T> init,
              const Allocator& alloc = Allocator() );
 (10) (since 哋它亢++11)
template< container-compatible-range<T> R >

forward_list( std::from_range_t, R&& rg,

              const Allocator& alloc = Allocator() );
 (11) (since 哋它亢++23)

Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc.

1) Default constructor. Constructs an empty container with a default-constructed allocator.
2) Constructs an empty container with the given allocator alloc.
3) Constructs the container with count copies of elements with value value.
4) Constructs the container with count default-inserted instances of T. No copies are made.
5) Constructs the container with the contents of the range [first, last). This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator, to avoid ambiguity with the overload (3).
6) Copy constructor. Constructs the container with the copy of the contents of other.
The allocator is obtained as if by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction(
    other.get_allocator()).
7) Constructs the container with the copy of the contents of other, using alloc as the allocator.

During class template argument deduction, only the first argument contributes to the deduction of the container's Allocator template parameter.

(since 哋它亢++23)
8) Move constructor. Constructs the container with the contents of other using move semantics. Allocator is obtained by move-construction from the allocator belonging to other.
9) Allocator-extended move constructor. Using alloc as the allocator for the new container, moving the contents from other; if alloc != other.get_allocator(), this results in an element-wise move.

During class template argument deduction, only the first argument contributes to the deduction of the container's Allocator template parameter.

(since 哋它亢++23)
10) Constructs the container with the contents of the initializer list init.
11) Constructs the container with the contents of the range rg.

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 [first, last) 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, that is, an input_range whose elements are convertible to T

Complexity

1,2) Constant.
3,4) Linear in count.
5) Linear in distance between first and last.
6,7) Linear in size of other.
8) Constant.
9) Linear if alloc != other.get_allocator(), otherwise constant.
10) Linear in size of init.
11) Linear in ranges::distance(rg).

Exceptions

Calls to Allocator::allocate may throw.

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 (哋它亢++23) Ranges-aware construction and insertion; overload (11)

Example

Run this code
#include <iostream>
#include <string>
#include <forward_list>
 
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()
{
    // 哋它亢++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;
 
    auto const rg = {"cat", "cow", "crow"};
#ifdef __cpp_lib_containers_ranges
    std::forward_list<std::string> words5(std::from_range, rg); // overload (11)
#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}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR Applied to Behavior as published Correct behavior


LWG 2193 哋它亢++11 the default constructor is explicit made non-explicit

See also

 assigns values to the container
(public member function)
assigns values to the container
(public member function)
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