advance

     Iterator Operation

Move an iterator forward or backward (if available) by a certain distance.

Contents

• Synopsis
• Description
• Example
• Warnings
• See Also

#include <iterator>

template <class InputIterator, class Distance>
void advance (InputIterator& i, Distance n);

The advance template function allows an iterator to be advanced through a container by some arbitrary distance. For bidirectional and random access iterators, this distance may be negative. This function uses operator+ and operator- for random access iterators, which provides a constant time implementation. For input, forward, and bidirectional iterators, advance uses operator ++ to provide linear time implementations. advance also uses operator -- with bidirectional iterators to provide linear time implementations of negative distances.

If n is positive, advance increments iterator reference i by n. For negative n, advance decrements reference i. Remember that advance accepts a negative argument n for random access and bidirectional iterators only.

//
// advance.cpp
//
 #include<iterator>
 #include<list>
 #include<iostream.h>
 int main()
 {
   //
   //Initialize a list using an array
   //
   int arr[6] = {3,4,5,6,7,8};
   list<int> l(arr,arr+6);
   //
   //Declare a list iterator, s.b. a ForwardIterator
   //
   list<int>::iterator itr = l.begin();
   //
   //Output the original list
   //
   cout << "For the list: ";
   copy(l.begin(),l.end(),ostream_iterator<int>(cout," "));
   cout << endl << endl;
   cout << "When the iterator is initialized to l.begin()," 
        << endl << "it points to " << *itr << endl << endl;
   //
   // operator+ is not available for a ForwardIterator, 
   // so use advance.
   //
   advance(itr, 4);
   cout << "After advance(itr,4), the iterator points to " 
        << *itr << endl;
   return 0;
 }
Output :
For the list: 3 4 5 6 7 8
When the iterator is initialized to l.begin(),
it points to 3
After advance(itr,4), the iterator points to 7

If your compiler does not support default template parameters then you need to always supply the Allocator template argument. For instance you'll have to write:

vector<int,allocator>

instead of:

vector<int>

Sequences, distance