1.2.2.2 Reverse iterator

• reverse_iterator topic: You need a front-to-back traversal or a back-to-front traversal. The reason for reverse iterators is that the standard algorithms do not know how to iterate over a collection backwards. For example:
  std::find(foo.begin(), foo.end(), L’a’); 
                    // Returns an iterator pointing 
                        // to the first a character. 
  std::find(foo.rbegin(), foo.rend(), L’a’).base()-1; 
                        //Returns an iterator 
                         // pointing to the last A. 
  std::find(foo.end(), foo.begin(), L’a’); 
                     //WRONG!! (Buffer overrun)
• reverse_iterator can use base() to change a normal iterator, because all the contain member function just receive normal iterator. such as insert and erase. why ri.base() and ri will have step 1 advance. detail can be seen effective stl item 28.
  reverse_iterator ri = 
      find(foo.rbegin(), foo.rend(), L’a’); 
  foo.insert(ri.base()); // you can use ri.base() directly. 
                                 // when you want to insert. 
  foo.erase((++ri).base()); //you can’t use ri.base() directly. 
                                   //when you erase what you want. 
        ri 
  1 2 3 4 5 
          i = ri.base()