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63 lines
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<TITLE>Error Indication by Stream Iterators</TITLE>
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<A HREF="43-2.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="43-4.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>
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<H2>43.3 Error Indication by Stream Iterators</H2>
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<A NAME="idx978"><!></A>
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<P>The <B><I><A HREF="../stdlibref/basic-istream.html">istream</A></I></B> and <B><I><A HREF="../stdlibref/basic-ostream.html">ostream</A></I></B> iterators by themselves have no means of indicating the success or failure of an operation. The stream being operated on should be probed for<SAMP> good()</SAMP>, <SAMP>eof()</SAMP>, <SAMP>fail()</SAMP>, or <SAMP>bad()</SAMP> conditions. This is convenient, as stream state can be checked for exception conditions that were set in <B><I><A HREF="../stdlibref/basic-ios.html">basic_ios</A></I></B> (using the member function <SAMP>exceptions(iostate)</SAMP>) after each input or output operation.</P>
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<UL><PRE>
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void print()
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{
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std::ostream_iterator<int, char, char_traits<char> > os(cout);
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try {
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std::cout.exceptions (std::ios::failbit | std::ios::badbit);
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*os = 3; //output `3'
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os++; // receive next output
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}
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catch(std::ios_base::failure& emsg) {
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std::cerr<<emsg.what();
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}
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}
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</PRE></UL>
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<P>Since stream buffers do not retain information about the success or failure of operations, <B><I><A HREF="../stdlibref/basic-streambuf.html">streambuf</A></I></B> iterators provide a member function, <SAMP>failed()</SAMP>, to indicate success or failure in a preceding operation on the stream buffer. </P>
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