<!--
    Licensed to the Apache Software  Foundation (ASF) under one or more
    contributor  license agreements.  See  the NOTICE  file distributed
    with  this  work  for  additional information  regarding  copyright
    ownership.   The ASF  licenses this  file to  you under  the Apache
    License, Version  2.0 (the  License); you may  not use  this file
    except in  compliance with the License.   You may obtain  a copy of
    the License at

    http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the  License is distributed on an  "AS IS" BASIS,
    WITHOUT  WARRANTIES OR CONDITIONS  OF ANY  KIND, either  express or
    implied.   See  the License  for  the  specific language  governing
    permissions and limitations under the License.

    Copyright 1999-2007 Rogue Wave Software, Inc.
-->

<HTML>
<HEAD>
<TITLE>Differences between Stream Iterators and Container Iterators</TITLE>
<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
<BODY BGCOLOR=#FFFFFF>
<A HREF="43-1.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="43-3.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library User's Guide</B></DIV>
<H2>43.2 Differences between Stream Iterators and Container Iterators</H2>
<A NAME="idx977"><!></A>
<P>In contrast to regular container iterators, stream iterators can provide only non-modifiable read-only access or write-only access to their elements. The <B><I><A HREF="../stdlibref/istream-iterator.html">istream_iterator</A></I></B> template is an InputIterator that can access but not modify elements. The <B><I><A HREF="../stdlibref/ostream-iterator.html">ostream_iterator</A></I></B> tempate, on the other hand, is an OutputIterator that provides write-only access to streams.</P>
<P>Each time the <B><I><A HREF="../stdlibref/istream-iterator.html">istream_iterator</A></I></B> object invokes <SAMP>operator++()</SAMP>, a new value from the stream is read and stored in value of type <SAMP>T,</SAMP> where <SAMP>T</SAMP> is the type of the element being written. The cached value, which by definition cannot be overwritten by assignment, is then available through the use of the dereferencing <SAMP>operator*()</SAMP>. This behavior of storing elements in the iterator is unique to <B><I>istream_iterator</I></B>s.</P>
<P>Also unlike container iterators, stream iterators can access elements only once, and only in the forward-moving direction, so that they can work only with one-pass algorithms. If the contents of the stream are to be read more than once, separate iterators must be created for each pass. Due to this unique nature of InputIterators it is inadvisable to use more than one <B><I><A HREF="../stdlibref/istream-iterator.html">istream_iterator</A></I></B> with the same stream object at the same time.</P>
<P>The <B><I><A HREF="../stdlibref/istream-iterator.html">istream_iterator</A></I></B> has a template parameter named <SAMP>Distance</SAMP>, with the default value of <SAMP>std::ptrdiff_t</SAMP> (which is defined in <SAMP>&lt;cstddef&gt;</SAMP>), although the <SAMP>Distance</SAMP> parameter is not used in the implementation. There is no distance type template argument for <B><I><A HREF="../stdlibref/ostream-iterator.html">ostream_iterator</A></I></B>, since pure OutputIterators do not have the notion of distance!</P>

<BR>
<HR>
<A HREF="43-1.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="43-3.html"><IMG SRC="images/bnext.gif" WIDTH=20 HEIGHT=21 ALT="Next file" BORDER=O></A>

<!-- Google Analytics tracking code -->
<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
    _uacct = "UA-1775151-1";
    urchinTracker();
</script>
<!-- end of Google Analytics tracking code -->

</BODY>
</HTML>