67 lines
3.8 KiB
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67 lines
3.8 KiB
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<TITLE>Implicit Synchronization by Tying Streams</TITLE>
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<A HREF="35-3.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="35-5.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>35.4 Implicit Synchronization by Tying Streams</H2>
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<A NAME="idx880"><!></A>
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<A NAME="idx881"><!></A>
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<P>Another mechanism for automatic synchronization in certain cases is tying a stream to an output stream, as demonstrated in the code below. All input or output operations flush the tied stream's buffer before they perform the actual operation.</P>
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<UL><PRE>
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std::ofstream ostr("/tmp/fil");
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std::ifstream istr("/tmp/fil");
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std::ostream* old_tie = istr.tie(&ostr); //1
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while (some_condition) {
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ostr << "... some output ...";
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std::string s;
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while (istr >> s) //2
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// process input ;
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}
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istr.tie(old_tie); //3
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</PRE></UL>
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<TABLE CELLPADDING="3">
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<TR VALIGN="top"><TD><SAMP>//1</SAMP></TD><TD>The input stream <SAMP>istr</SAMP> is tied to the output stream <SAMP>ostr</SAMP>. The <SAMP>tie()</SAMP> member function returns a pointer to the previously tied output stream, or <SAMP>0</SAMP> if no output stream is tied.
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<TR VALIGN="top"><TD><SAMP>//2</SAMP></TD><TD>Before any input is done, the tied output stream's buffer is flushed so that the result of previous output operations to <SAMP>ostr</SAMP> is available in the external file <SAMP>/tmp/fil</SAMP>.
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<TR VALIGN="top"><TD><SAMP>//3</SAMP></TD><TD>The previous tie is restored.
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