.. Iterators/Iterator Metafunctions//distance |20

distance

Synopsis

.. parsed-literal::

template<
      typename First
    , typename Last
    >
struct distance
{
    typedef |unspecified| type;
};

Description

Returns the distance between First and Last iterators, that is, an |Integral Constant| n such that advance<First,n>::type is identical to Last.

Header

.. parsed-literal::

#include <boost/mpl/distance.hpp>

Parameters

+---------------+---------------------------+-----------------------------------+ | Parameter | Requirement | Description | +===============+===========================+===================================+ | First, | |Forward Iterator| | Iterators to compute a | | Last | | distance between. | +---------------+---------------------------+-----------------------------------+

Model Of

|Tag Dispatched Metafunction|

Expression semantics

For any |Forward Iterator|\ s first and last:

.. parsed-literal::

typedef distance<first,last>::type n; 

:Return type: |Integral Constant|.

:Precondition: [first, last) is a valid range.

:Semantics: Equivalent to

.. parsed-literal::

    typedef iter_fold<
          iterator_range<first,last>
        , long_<0>
        , next<_1>
        >::type n;
    

:Postcondition: is_same< advance<first,n>::type, last >::value == true.

Complexity

Amortized constant time if first and last are |Random Access Iterator|\ s, otherwise linear time.

Example

.. parsed-literal::

typedef range_c<int,0,10>::type range;
typedef begin<range>::type first;
typedef end<range>::type last;

BOOST_MPL_ASSERT_RELATION( (distance<first,last>::value), ==, 10);

See also

|Iterators|, |Tag Dispatched Metafunction|, |advance|, |next|, |prior|

.. copyright:: Copyright 2001-2009 Aleksey Gurtovoy and David Abrahams Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)