#include <string>
  TYPE& at( size_type loc );
  const TYPE& at( size_type loc ) const;

The at() function returns a reference to the element in the string at index loc. The at() function is safer than the [] operator, because it won't let you reference items outside the bounds of the string.

For example, consider the following code:

 vector<int> v( 5, 1 );
 for( int i = 0; i < 10; i++ ) {
   cout << "Element " << i << " is " << v[i] << endl;
 }              

This code overrunns the end of the vector, producing potentially dangerous results. The following code would be much safer:

 vector<int> v( 5, 1 );
 for( int i = 0; i < 10; i++ ) {
   cout << "Element " << i << " is " << v.at(i) << endl;
 }              

Instead of attempting to read garbage values from memory, the at() function will realize that it is about to overrun the vector and will throw an exception.