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std::forward_list::forward_list

From cppreference.com

[edit template]
 
C++
 
Containers library
 
std::forward_list
 
forward_list();
explicit forward_list( const Allocator& alloc );
 (1)
forward_list( size_type count,

              const T& value,

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

forward_list( InputIt first, InputIt last,

              const Allocator& alloc = Allocator() );
 (4) (since C++11)
forward_list( const forward_list& other );
 (5) (since C++11)
forward_list( const forward_list& other, const Allocator& alloc );
 (5) (since C++11)
forward_list( forward_list&& other );
 (6) (since C++11)
forward_list( forward_list&& other, const Allocator& alloc );
 (7) (since C++11)
forward_list( std::initializer_list<T> init,
              const Allocator& alloc = Allocator() );
 (8) (since C++11)

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

1) Default constructor. Constructs an empty container. If no allocator is supplied, allocator is obtained from a default-constructed instance.
2) Constructs the container with count copies of elements with value value.
3) Constructs the container with count default-inserted instances of T. No copies are made.
4) Constructs the container with the contents of the range [first, last).
This constructor has the same effect as forward_list(static_cast<size_type>(first), static_cast<value_type>(last), a) if InputIt is an integral type. (until C++11)
This overload only participates in overload resolution if InputIt satisfies InputIterator, to avoid ambiguity with the overload (2). (since C++11)
5) Copy constructor. Constructs the container with the copy of the contents of other. If alloc is not provided, allocator is obtained as if by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction(other.get_allocator()).
6) 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.
7) 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.
8) Constructs the container with the contents of the initializer list init.

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

[edit] Complexity

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

[edit] Exceptions

Calls to Allocator::allocate may throw.

[edit] Notes

After container move construction (overload (6)), 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 §23.2.1[container.requirements.general]/12, and a more direct guarantee is under consideration via LWG 2321.


[edit] Example

Run this code
#include <forward_list>
#include <string>
#include <iostream>
 
template<typename T>
std::ostream& operator<<(std::ostream& s, const std::forward_list<T>& v) {
    s.put('[');
    char comma[3] = {'\0', ' ', '\0'};
    for (const auto& e : v) {
        s << comma << e;
        comma[0] = ',';
    }
    return s << ']';
}
 
int main() 
{
    // c++11 initializer list syntax:
    std::forward_list<std::string> words1 {"the", "frogurt", "is", "also", "cursed"};
    std::cout << "words1: " << words1 << '\n';
 
    // words2 == words1
    std::forward_list<std::string> words2(words1.begin(), words1.end());
    std::cout << "words2: " << words2 << '\n';
 
    // words3 == words1
    std::forward_list<std::string> words3(words1);
    std::cout << "words3: " << words3 << '\n';
 
    // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"}
    std::forward_list<std::string> words4(5, "Mo");
    std::cout << "words4: " << words4 << '\n';
}

Output: 

words1: [the, frogurt, is, also, cursed]
words2: [the, frogurt, is, also, cursed]
words3: [the, frogurt, is, also, cursed]
words4: [Mo, Mo, Mo, Mo, Mo]

[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 is explicit made non-explicit

[edit] See also

 assigns values to the container
(public member function) [edit]
assigns values to the container
(public member function) [edit]
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