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<TITLE>__distance_type()</TITLE>
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<H2>__distance_type()</H2><PRE><HR><B><I>Does not inherit</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">See Also</A></LI>
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<A NAME="sec1"><H3>Local Index</H3></A>
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<A NAME="sec2"><H3>Summary</H3></A>
<P>A function that determines the type of distance used by an iterator. </P>
<BLOCKQUOTE><HR><B>
NOTE -- This function is now obsolete. It is retained here to<br>support compilers that do not include partial specialization, but<br>will be dropped in a subsequent release.
</B><HR></BLOCKQUOTE>
<A NAME="sec3"><H3>Synopsis</H3></A>

<UL><PRE>#include &lt;iterator&gt;
template &lt;class Category, class T, class Distance, 
          class Pointer, class Reference&gt;
inline Distance* 
       __distance_type(const iterator&lt;Category, T,
                         Distance, Pointer, Reference&gt;&amp;);
template &lt;class T&gt;
inline ptrdiff_t* __distance_type(const T*);
</PRE></UL>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <SAMP>__distance_type()</SAMP> family of function templates returns a pointer to a value that is of the same type as that used to represent a distance between two iterators. The first of these takes an iterator of a particular type and returns a pointer to a default value of the <B><I>difference_type</I></B> for that iterator. The <SAMP>T*</SAMP> form of the function returns <SAMP>ptrdiff_t*</SAMP>.</P>
<P>Generic algorithms use this function to create local variables of the correct type. The <SAMP>__distance_type()</SAMP> functions are typically used like this:</P>

<UL><PRE>template &lt;class Iterator&gt;
void foo(Iterator start, Iterator finish)
{
  __foo(begin,end,__distance_type(first));
}

template &lt;class Iterator, class Distance&gt;
void __foo(Iterator start, Iterator finish, Distance*&gt;
{
  Distance d = Distance();
  distance(start,finish,d);
  ...
}
</PRE></UL>
<P>The auxiliary function template allows the algorithm to extract a distance type from the first iterator and then use that type to perform some useful work.</P>
<A NAME="sec5"><H3>See Also</H3></A>
<P>Other iterator primitives:  <SAMP><A HREF="--iterator-category.html">__iterator_category()</A></SAMP>, <SAMP><A HREF="distance.html">distance()</A></SAMP>, <SAMP><A HREF="advance.html">advance()</A></SAMP></P>

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