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diff --git a/gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt11ch28s02.html b/gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt11ch28s02.html new file mode 100644 index 000000000..5e668931c --- /dev/null +++ b/gcc-4.4.3/libstdc++-v3/doc/html/manual/bk01pt11ch28s02.html @@ -0,0 +1,49 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Performance</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="io_and_c.html" title="Chapter 28. Interacting with C" /><link rel="prev" href="io_and_c.html" title="Chapter 28. Interacting with C" /><link rel="next" href="extensions.html" title="Part XII. Extensions" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Performance</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="io_and_c.html">Prev</a> </td><th width="60%" align="center">Chapter 28. Interacting with C</th><td width="20%" align="right"> <a accesskey="n" href="extensions.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.io.c.sync"></a>Performance</h2></div></div></div><p> + Pathetic Performance? Ditch C. + </p><p>It sounds like a flame on C, but it isn't. Really. Calm down. + I'm just saying it to get your attention. + </p><p>Because the C++ library includes the C library, both C-style and + C++-style I/O have to work at the same time. For example: + </p><pre class="programlisting"> + #include <iostream> + #include <cstdio> + + std::cout << "Hel"; + std::printf ("lo, worl"); + std::cout << "d!\n"; + </pre><p>This must do what you think it does. + </p><p>Alert members of the audience will immediately notice that buffering + is going to make a hash of the output unless special steps are taken. + </p><p>The special steps taken by libstdc++, at least for version 3.0, + involve doing very little buffering for the standard streams, leaving + most of the buffering to the underlying C library. (This kind of + thing is tricky to get right.) + The upside is that correctness is ensured. The downside is that + writing through <code class="code">cout</code> can quite easily lead to awful + performance when the C++ I/O library is layered on top of the C I/O + library (as it is for 3.0 by default). Some patches have been applied + which improve the situation for 3.1. + </p><p>However, the C and C++ standard streams only need to be kept in sync + when both libraries' facilities are in use. If your program only uses + C++ I/O, then there's no need to sync with the C streams. The right + thing to do in this case is to call + </p><pre class="programlisting"> + #include <span class="emphasis"><em>any of the I/O headers such as ios, iostream, etc</em></span> + + std::ios::sync_with_stdio(false); + </pre><p>You must do this before performing any I/O via the C++ stream objects. + Once you call this, the C++ streams will operate independently of the + (unused) C streams. For GCC 3.x, this means that <code class="code">cout</code> and + company will become fully buffered on their own. + </p><p>Note, by the way, that the synchronization requirement only applies to + the standard streams (<code class="code">cin</code>, <code class="code">cout</code>, + <code class="code">cerr</code>, + <code class="code">clog</code>, and their wide-character counterparts). File stream + objects that you declare yourself have no such requirement and are fully + buffered. + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="io_and_c.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="io_and_c.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="extensions.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 28. Interacting with C </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Part XII. + Extensions + +</td></tr></table></div></body></html> |