public member function
<vector>

std::vector::push_back

void push_back (const value_type& val);

void push_back (const value_type& val);
void push_back (value_type&& val);
Add element at the end
Adds a new element at the end of the vector, after its current last element. The content of val is copied (or moved) to the new element.

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.

Parameters

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

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::push_back
#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector;
  int myint;

  std::cout << "Please enter some integers (enter 0 to end):\n";

  do {
    std::cin >> myint;
    myvector.push_back (myint);
  } while (myint);

  std::cout << "myvector stores " << int(myvector.size()) << " numbers.\n";

  return 0;
}

The example uses push_back to add a new element to the vector each time a new integer is read.

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 the container are invalidated.
Otherwise, only the end iterator is invalidated, and all 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.

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 val as argument, it causes undefined behavior.

See also

vector::pop_back
Delete last element (public member function )
vector::insert
Insert elements (public member function )

C++