distance (3C++std) - Tru64 UNIX
Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc. NAME
distance - Computes the distance between two iterators
SYNOPSIS
#include <iterator>
template <class ForwardIterator>
iterator_traits<ForwardIterator>::distance_type
distance (ForwardIterator first,
ForwardIterator last);
template <class ForwardIterator, class Distance>
void distance (ForwardIterator first,
ForwardIterator last,
Distance& n);
DESCRIPTION
The distance template function computes the distance between two iterator.
The first version returns that value, while the second version increments n
by that value. The last iterator must be reachable from the first
iterator.
Note that the second version of this function is obsolete. It is provided
for backward compatibility and to support compilers that do not provide
partial specialization. As you may have already deduced, the first version
of the function is not available with compilers that do not support partial
specialization since it depends on iterator_traits, which itself depends on
that particular language feature.
EXAMPLE
//
// distance.cpp
//
#include <iterator>
#include <vector>
#include <iostream.h>
int main()
{
//
//Initialize a vector using an array
//
int arr[6] = {3,4,5,6,7,8};
vector<int> v(arr,arr+6);
//
//Declare a list iterator, s.b. a ForwardIterator
//
vector<int>::iterator itr = v.begin()+3;
//
//Output the original vector
//
cout << "For the vector: ";
copy(v.begin(),v.end(),
ostream_iterator<int,char>(cout," "));
cout << endl << endl;
cout << "When the iterator is initialized to point to "
<< *itr << endl;
//
// Use of distance
//
vector<int>::difference_type dist = 0;
distance(v.begin(), itr, dist);
cout << "The distance between the beginning and itr is "
<< dist << endl;
return 0;
}
Output :
For the vector: 3 4 5 6 7 8
When the iterator is initialized to point to 6
The distance between the beginning and itr is 3
WARNING
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,int> > instead of:
vector <int>
Also, if your compiler does not support partial specialization then you
will not be able to use the version of distance that returns the distance.
Instead you'll have to use the version that increments a reference
parameter.
SEE ALSO
sequence, random_iterator
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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