const_reference at ( size_type n ) const;
      reference at ( size_type n );

Access element

Returns a reference to the element at position n in the vector.

The difference between this member function and member operator function operator[] is that vector::at signals if the requested position is out of range by throwing an out_of_range exception.

Parameters

n

Position of an element in the vector.
If this is greater than the vector size, an exception of type out_of_range is thrown.
Notice that the first element has a position of 0, not 1.
Member type size_type is an unsigned integral type.

Return value

Member types reference and const_reference are the reference types to the elements of the vector container (for the default storage allocation model, allocator, these are T& and const T& respectively).

Example

// vector::at
#include <iostream>
#include <vector>
using namespace std;

int main ()
{
  vector<int> myvector (10);   // 10 zero-initialized ints
  unsigned int i;

  // assign some values:
  for (i=0; i<myvector.size(); i++)
    myvector.at(i)=i;

  cout << "myvector contains:";
  for (i=0; i<myvector.size(); i++)
    cout << " " << myvector.at(i);

  cout << endl;

  return 0;
}

Output:

myvector contains: 0 1 2 3 4 5 6 7 8 9

Complexity

See also