public member function
<vector>

std::vector::front

      reference front();
const_reference front() const;
Access first element
Returns a reference to the first element in the vector.

Unlike member vector::begin, which returns an iterator to this same element, this function returns a direct reference.

Calling this function on an empty container causes undefined behavior.

Parameters

none

Return value

A reference to the first element in the vector container.

If the vector object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.

Member types reference and const_reference are the reference types to the elements of the container (see vector member types).

Example

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// vector::front
#include <iostream>
#include <vector>

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

  myvector.push_back(78);
  myvector.push_back(16);

  // now front equals 78, and back 16

  myvector.front() -= myvector.back();

  std::cout << "myvector.front() is now " << myvector.front() << '\n';

  return 0;
}


Output:
myvector.front() is now 62

Complexity

Constant.

Iterator validity

No changes.

Data races

The container is accessed (neither the const nor the non-const versions modify the container).
The reference returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.

Exception safety

If the container is not empty, the function never throws exceptions (no-throw guarantee).
Otherwise, 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