first commit
This commit is contained in:
Jose Caban
72
extern/stdcxx/4.2.1/doc/stdlibug/29-3.html
vendored
Normal file
72
extern/stdcxx/4.2.1/doc/stdlibug/29-3.html
vendored
Normal file
@@ -0,0 +1,72 @@
|
||||
<!--
|
||||
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>Catching Exceptions</TITLE>
|
||||
<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
|
||||
<BODY BGCOLOR=#FFFFFF>
|
||||
<A HREF="29-2.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="30.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>29.3 Catching Exceptions</H2>
|
||||
<A NAME="idx736"><!></A>
|
||||
<A NAME="idx737"><!></A>
|
||||
<P>By default a stream does not throw any exceptions. You must explicitly activate an exception because a stream contains an<I> exception mask</I>. Each flag in this mask corresponds to one of the error flags. For example, once the <SAMP>badbit</SAMP> flag is set in the exception mask, an exception is thrown each time the <SAMP>badbit</SAMP> flag is set in the stream state.</P>
|
||||
<BLOCKQUOTE><HR><B>
|
||||
NOTE -- An example of using an exception mask is provided by the streams layer, which catches <SAMP>bad_alloc</SAMP> exceptions thrown during allocation of its internal resources, <SAMP>iword</SAMP> and <SAMP>pword</SAMP><B>. </B>It then sets<B> </B><SAMP>badbit</SAMP> or <SAMP>failbit</SAMP><B>. </B>An exception would be thrown only if the corresponding bit in the exception mask is set. The exception thrown is<B> </B><SAMP>ios_base::failure</SAMP><B>.</B>
|
||||
</B><HR></BLOCKQUOTE>
|
||||
<A NAME="idx738"><!></A>
|
||||
<P>The following code demonstrates how to activate an exception on an input stream object <SAMP>in</SAMP>:</P>
|
||||
|
||||
<UL><PRE>
|
||||
extern std::istream& in;
|
||||
try {
|
||||
in.exceptions(std::ios_base::badbit |
|
||||
std::ios_base::failbit); //1
|
||||
in >> x;
|
||||
// do lots of other stream i/o
|
||||
}
|
||||
catch(std::ios_base::failure& exc) { //2
|
||||
std::cerr << exc.what() << std::endl;
|
||||
throw;
|
||||
}
|
||||
</PRE></UL>
|
||||
<TABLE CELLPADDING="3">
|
||||
|
||||
<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>In calling the <SAMP>exceptions()</SAMP> function, you indicate what flags in the stream's state shall cause an exception to be thrown. [Each change of either the stream state or the exception mask can result in an exception being thrown. This is because the functions <SAMP>setstate()</SAMP> and <SAMP>exception()</SAMP> raise an exception in case the exception mask requires it.]
|
||||
<TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>Objects thrown by the stream's operations are of types derived from <SAMP>std::ios_base::failure</SAMP>. Hence this catch clause catches all stream exceptions in principle. We qualify this generalization because a stream might fail to catch certain exceptions like <SAMP>std::bad_alloc</SAMP>, for example, so that exceptions other than <SAMP>std::ios_base::failure</SAMP> might be raised. That's how exception handling in C++ works: you never know what exceptions will be raised.
|
||||
</TABLE>
|
||||
<A NAME="idx739"><!></A>
|
||||
<P>Generally, it is a good idea to activate the <SAMP>badbit</SAMP> exception and suppress the <SAMP>eofbit</SAMP> and <SAMP>failbit</SAMP> exceptions, because the latter do not represent exceptional states. A <SAMP>badbit</SAMP> situation, however, is likely to be a serious error condition similar to the memory shortage indicated by a <SAMP>bad_alloc</SAMP> exception. Unless you want to suppress exceptions thrown by iostreams altogether, we would recommend that you switch on the <SAMP>badbit</SAMP> exception and turn off <SAMP>eofbit</SAMP> and <SAMP>failbit</SAMP>.</P>
|
||||
|
||||
<BR>
|
||||
<HR>
|
||||
<A HREF="29-2.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="30.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>
|
||||
Reference in New Issue
Block a user