public member function
<list>

std::list::emplace

template <class... Args>
  iterator emplace (const_iterator position, Args&&... args);
Construct and insert element
The container is extended by inserting a new element at position. This new element is constructed in place using args as the arguments for its construction.

This effectively increases the container size by one.

Unlike other standard sequence containers, list and forward_list objects are specifically designed to be efficient inserting and removing elements in any position, even in the middle of the sequence.

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

A similar member function exists, insert, which either copies or moves existing objects into the container.

Parameters

position
Position in the container where the new element is inserted.
Member type const_iterator is a bidirectional iterator type that points to a const element.
args
Arguments forwarded to construct the new element.

Return value

An iterator that points to the newly emplaced element.

Member type iterator is a bidirectional iterator type that points to an element.

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

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// list::emplace
#include <iostream>
#include <list>

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

  mylist.emplace ( mylist.begin(), 100, 'x' );
  mylist.emplace ( mylist.begin(), 200, 'y' );

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

  std::cout << '\n';
  return 0;
}

Output:
mylist contains: (200,y) (100,x)

Complexity

Constant.

Iterator validity

No changes.

Data races

The container is modified.
No contained elements are accessed: concurrently accessing or modifying them is safe, although iterating ranges that include position is not.

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, or if position is not valid, 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