itera o vetor do fim para começar

for ( vector<int>::reverse_iterator i = my_vector.rbegin(); 
        i != my_vector.rend(); ++i ) { 
}

OR

vector<my_class>::iterator i = my_vector.end();
while (i != my_vector.begin())
{
     --i;
    /*do stuff */

} 
Wide-eyed Weevil