public member function
<list>

std::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 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.

The element is constructed in-place by calling allocator_traits::construct with args forwarded.

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 elements is allocated using the container's allocator, which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).

Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
// list::emplace_front
#include <iostream>
#include <list>

int main ()
{
  std::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

  • 9316991614 2018-02-25
  • 191841613 2018-02-25
  • 16411612 2018-02-25
  • 6081981611 2018-02-25
  • 1784561610 2018-02-25
  • 4651609 2018-02-25
  • 9348111608 2018-02-25
  • 2513771607 2018-02-25
  • 6478461606 2018-02-24
  • 4985791605 2018-02-24
  • 5637141604 2018-02-24
  • 282181603 2018-02-24
  • 6217941602 2018-02-24
  • 5076141601 2018-02-24
  • 714281600 2018-02-24
  • 6607141599 2018-02-24
  • 949041598 2018-02-24
  • 6809961597 2018-02-24
  • 671871596 2018-02-24
  • 7107821595 2018-02-24