public member function
<forward_list>

std::forward_list::push_front

void push_front (const value_type& val);
void push_front (value_type&& val);
Insert element at beginning
Inserts a new element at the beginning of the forward_list, right before its current first element. The content of val is copied (or moved) to the inserted element.

This effectively increases the container size by one.

A similar member function exists, emplace_front, which constructs the inserted element object directly in place, without performing any copy or move operation.

Parameters

val
Value to be copied (or moved) to the inserted element.
Member type value_type is the type of the elements in the container, defined in forward_list as an alias of its first template parameter (T).

Return value

none

If storage is needed for the new element, it 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::push_front
#include <iostream>
#include <forward_list>
using namespace std;

int main ()
{
  forward_list<int> mylist = {77, 2, 16};
  mylist.push_front (19);
  mylist.push_front (34);

  std::cout << "mylist contains:";
  for (int& x: mylist) std::cout << ' ' << x;
  std::cout << '\n';

  return 0;
}


Output:
mylist contains: 34 19 77 2 16

Complexity

Constant.

Iterator validity

No changes.

Data races

The container is modified.
No existing 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 val as argument, 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