public member function
<forward_list>

std::forward_list::emplace_front

template <class... Args>
  void emplace_front (Args&&... args);
Construct and insert element at beginning
Inserts a new element at the beginning of the forward_list, right before its current first element. This new element is constructed in place using args as the arguments for its construction.

This effectively increases the container size by one.

A similar member function exists, push_front, which either copies or moves an existing object into the container.

Parameters

args
Arguments forwarded to construct the new element.

Return value

none

The storage for the new element is allocated using allocator_traits<allocator_type>::construct(), which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).

Example

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// forward_list::emplace_front
#include <iostream>
#include <forward_list>

int main ()
{
  std::forward_list< std::pair<int,char> > mylist;

  mylist.emplace_front(10,'a');
  mylist.emplace_front(20,'b');
  mylist.emplace_front(30,'c');

  std::cout << "mylist contains:";
  for (auto& x: mylist)
    std::cout << " (" << x.first << "," << x.second << ")";

  std::cout << std::endl;
  return 0;
}


Output:
mylist contains: (30,c) (20,b) (10,a) 

Complexity

Constant.

Iterator validity

No changes.
Member begin returns a different iterator value.

Data races

The container is modified.
No contained elements are accessed: concurrently accessing or modifying them is safe.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.
If allocator_traits::construct is not supported with the appropriate arguments, it causes undefined behavior.

See also

  • 997351548 2018-02-20
  • 903691547 2018-02-20
  • 9127171546 2018-02-20
  • 2234751545 2018-02-20
  • 1685381544 2018-02-20
  • 911091543 2018-02-20
  • 9281021542 2018-02-20
  • 632231541 2018-02-20
  • 9751491540 2018-02-20
  • 8333621539 2018-02-20
  • 995001538 2018-02-20
  • 6477441537 2018-02-20
  • 511981536 2018-02-19
  • 2072881535 2018-02-19
  • 6024461534 2018-02-19
  • 7594061533 2018-02-19
  • 9311341532 2018-02-19
  • 4928331531 2018-02-19
  • 38561530 2018-02-19
  • 7776611529 2018-02-19