public member function
<vector>

std::vector::emplace_back

template <class... Args>
  void emplace_back (Args&&... args);
Construct and insert element at the end
Inserts a new element at the end of the vector, right after its current last element. This new element is constructed in place using args as the arguments for its constructor.

This effectively increases the container size by one, which causes an automatic reallocation of the allocated storage space if -and only if- the new vector size surpasses the current vector capacity.

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

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

Parameters

args
Arguments forwarded to construct the new element.

Return value

none.

If a reallocation happens, the storage 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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// vector::emplace_back
#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector = {10,20,30};

  myvector.emplace_back (100);
  myvector.emplace_back (200);

  std::cout << "myvector contains:";
  for (auto& x: myvector)
    std::cout << ' ' << x;
  std::cout << '\n';

  return 0;
}

Output:
myvector contains: 10 20 30 100 200

Complexity

Constant (amortized time, reallocation may happen).

If a reallocation happens, the reallocation is itself up to linear in the entire size.

Iterator validity

If a reallocation happens, all iterators, pointers and references related to this container are invalidated.
Otherwise, only the end iterator is invalidated, and all other iterators, pointers and references to elements are guaranteed to keep referring to the same elements they were referring to before the call.

Data races

The container is modified.
If a reallocation happens, all contained elements are modified.
Otherwise, no existing element is accessed, and concurrently accessing or modifying them is safe (although see iterator validity above).

Exception safety

If no reallocations happen, there are no changes in the container in case of exception (strong guarantee).
If a reallocation happens, the strong guarantee is also given if the type of the elements is either copyable or no-throw moveable.
Otherwise, the container is guaranteed to end in a valid state (basic guarantee).
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