doc/stdlibug/38-2.html - stdcxx - Git at Google

 <!--
     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>Choosing a Base Class</TITLE>
 <LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
 <BODY BGCOLOR=#FFFFFF>
 <A HREF="38-1.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="38-3.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>38.2 Choosing a Base Class</H2>
 <A NAME="idx901"><!></A>
 <A NAME="idx902"><!></A>
 <P>The first question is: Which of the standard stream classes shall be the base class? The answer fully depends on the kind of addition or modification you want to make. In our case, we want to add formatting information, which depends on the stream's character type since the format string is a sequence of narrow characters. As we show later on, the format string must be expanded into a sequence of the stream's character type for use with the stream's locale. Consequently, a good choice for a base class is a specialization of <SAMP>std::basic_iostream</SAMP>, and since we want the format string to impact only output operations, the best choice is <SAMP>std::basic_ostream</SAMP>. </P>
 <P>In general, you choose a base class by looking at the kind of addition or modification you want to make and comparing it with the characteristics of the stream classes.</P>
 <UL>
 <LI><P CLASS="LIST">Choose the class <SAMP>std::ios_base</SAMP> if you add information and services that do not depend on the stream's character type.</P></LI>
 <LI><P CLASS="LIST">Choose the class template <SAMP>std::basic_ios</SAMP> (or a specialization thereof) if the added information does depend on the character type, or requires other information not available in <SAMP>ios_base</SAMP>, such as the stream buffer.</P></LI>
 <LI><P CLASS="LIST">Derive from the stream class templates <SAMP>std::basic_istream</SAMP>, <SAMP>std::basic_ostream</SAMP>, or <SAMP>std::basic_iostream</SAMP> if you want to add or change the input and output operations.</P></LI>
 <LI><P CLASS="LIST">Derive from the stream class templates <SAMP>std::basic_{i,o}fstream</SAMP>, or <SAMP>std::basic_{i,o}stringstream </SAMP>(or a specialization of one of these class templates) if you want to add or modify behavior that is file- or string-related, such as the way a file is opened.</P></LI>
 </UL>
 <P>Derivations from <SAMP>std::basic_istream</SAMP>, <SAMP>std::basic_ostream</SAMP>, or <SAMP>std::basic_iostream</SAMP> are the most common cases, because you typically want to modify or add input and output operations. </P>
 <P>If you derive from <SAMP>std::ios_base</SAMP> or <SAMP>std::basic_ios,</SAMP> you do not inherit any input and output operations; you do this if you really want to reimplement all of them or intend to implement a completely different kind of input or output operation, such as unformatted binary input and output.</P>
 <P>Derivations from file or string streams such as <SAMP>basic_{i,o}fstream</SAMP> or <SAMP>basic_{i,o}stringstream </SAMP>are equally rare, because they make sense only if file- or string-related data or services must be added or modified.</P>
 <BLOCKQUOTE><HR><B>
 NOTE -- Choose basic_istream, basic_ostream, or basic_iostream as a base class when deriving new stream classes, unless you have good reason not to do so.
 </B><HR></BLOCKQUOTE>

 <BR>
 <HR>
 <A HREF="38-1.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="38-3.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>
	<!--
	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>Choosing a Base Class</TITLE>
	<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
	<BODY BGCOLOR=#FFFFFF>
	<A HREF="38-1.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="38-3.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>38.2 Choosing a Base Class</H2>
	<A NAME="idx901"><!></A>
	<A NAME="idx902"><!></A>
	<P>The first question is: Which of the standard stream classes shall be the base class? The answer fully depends on the kind of addition or modification you want to make. In our case, we want to add formatting information, which depends on the stream's character type since the format string is a sequence of narrow characters. As we show later on, the format string must be expanded into a sequence of the stream's character type for use with the stream's locale. Consequently, a good choice for a base class is a specialization of <SAMP>std::basic_iostream</SAMP>, and since we want the format string to impact only output operations, the best choice is <SAMP>std::basic_ostream</SAMP>. </P>
	<P>In general, you choose a base class by looking at the kind of addition or modification you want to make and comparing it with the characteristics of the stream classes.</P>
	<UL>
	<LI><P CLASS="LIST">Choose the class <SAMP>std::ios_base</SAMP> if you add information and services that do not depend on the stream's character type.</P></LI>
	<LI><P CLASS="LIST">Choose the class template <SAMP>std::basic_ios</SAMP> (or a specialization thereof) if the added information does depend on the character type, or requires other information not available in <SAMP>ios_base</SAMP>, such as the stream buffer.</P></LI>
	<LI><P CLASS="LIST">Derive from the stream class templates <SAMP>std::basic_istream</SAMP>, <SAMP>std::basic_ostream</SAMP>, or <SAMP>std::basic_iostream</SAMP> if you want to add or change the input and output operations.</P></LI>
	<LI><P CLASS="LIST">Derive from the stream class templates <SAMP>std::basic_{i,o}fstream</SAMP>, or <SAMP>std::basic_{i,o}stringstream </SAMP>(or a specialization of one of these class templates) if you want to add or modify behavior that is file- or string-related, such as the way a file is opened.</P></LI>
	</UL>
	<P>Derivations from <SAMP>std::basic_istream</SAMP>, <SAMP>std::basic_ostream</SAMP>, or <SAMP>std::basic_iostream</SAMP> are the most common cases, because you typically want to modify or add input and output operations. </P>
	<P>If you derive from <SAMP>std::ios_base</SAMP> or <SAMP>std::basic_ios,</SAMP> you do not inherit any input and output operations; you do this if you really want to reimplement all of them or intend to implement a completely different kind of input or output operation, such as unformatted binary input and output.</P>
	<P>Derivations from file or string streams such as <SAMP>basic_{i,o}fstream</SAMP> or <SAMP>basic_{i,o}stringstream </SAMP>are equally rare, because they make sense only if file- or string-related data or services must be added or modified.</P>
	<BLOCKQUOTE><HR><B>
	NOTE -- Choose basic_istream, basic_ostream, or basic_iostream as a base class when deriving new stream classes, unless you have good reason not to do so.
	</B><HR></BLOCKQUOTE>

	<BR>
	<HR>
	<A HREF="38-1.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="38-3.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>