distance

Determines the number of increments between the positions addressed by two iterators.

template<class InputIterator>
   typename iterator_traits<InputIterator>::difference_type
      distance(
         InputIterator _First, 
         InputIterator _Last
      );

Parameters

• _First
  The first iterator whose distance from the second is to be determined.

• _Last
  The second iterator whose distance from the first is to be determined.

Return Value

The number of times that _First must be incremented until it equal _Last.

Remarks

The distance function has constant complexity when InputIterator satisfies the requirements for a random-access iterator; otherwise, it has linear complexity and so is potentially expensive.

Example

// iterator_distance.cpp
// compile with: /EHsc
#include <iterator>
#include <list>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   list<int> L;
   for ( i = -1 ; i < 9 ; ++i ) 
   {
      L.push_back ( 2 * i );
   }
   list <int>::iterator L_Iter, LPOS = L.begin ( );

   cout << "The list L is: ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++ )
      cout << *L_Iter << " ";
   cout << ")." << endl;
   
   cout << "The iterator LPOS initially points to the first element: "
        << *LPOS << "." << endl;

   advance ( LPOS , 7 );
   cout << "LPOS is advanced 7 steps forward to point "
        << " to the eighth element: "
        << *LPOS << "." << endl;

   list<int>::difference_type Ldiff ;
   Ldiff = distance ( L.begin ( ) , LPOS );
   cout << "The distance from L.begin( ) to LPOS is: "
        << Ldiff << "." << endl;
}

The list L is: ( -2 0 2 4 6 8 10 12 14 16 ).
The iterator LPOS initially points to the first element: -2.
LPOS is advanced 7 steps forward to point  to the eighth element: 12.
The distance from L.begin( ) to LPOS is: 7.

Requirements

Header: <iterator>

Namespace: std

See Also

Reference

distance (STL Samples)

Standard Template Library

Other Resources

<iterator> Members