1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 39. Input and Output</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="extensions.html" title="Part XII. Extensions" /><link rel="prev" href="ext_iterators.html" title="Chapter 38. Iterators" /><link rel="next" href="ext_demangling.html" title="Chapter 40. Demangling" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 39. Input and Output</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_iterators.html">Prev</a> </td><th width="60%" align="center">Part XII. 4 Extensions 5 6</th><td width="20%" align="right"> <a accesskey="n" href="ext_demangling.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 39. Input and Output"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.io"></a>Chapter 39. Input and Output</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ext_io.html#manual.ext.io.filebuf_derived">Derived filebufs</a></span></dt></dl></div><p> 7 Extensions allowing <code class="code">filebuf</code>s to be constructed from 8 "C" types like FILE*s and file descriptors. 9 </p><div class="sect1" title="Derived filebufs"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.io.filebuf_derived"></a>Derived filebufs</h2></div></div></div><p>The v2 library included non-standard extensions to construct 10 <code class="code">std::filebuf</code>s from C stdio types such as 11 <code class="code">FILE*</code>s and POSIX file descriptors. 12 Today the recommended way to use stdio types with libstdc++ 13 IOStreams is via the <code class="code">stdio_filebuf</code> class (see below), 14 but earlier releases provided slightly different mechanisms. 15 </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>3.0.x <code class="code">filebuf</code>s have another ctor with this signature: 16 <code class="code">basic_filebuf(__c_file_type*, ios_base::openmode, int_type); 17 </code> 18 This comes in very handy in a number of places, such as 19 attaching Unix sockets, pipes, and anything else which uses file 20 descriptors, into the IOStream buffering classes. The three 21 arguments are as follows: 22 </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p><code class="code">__c_file_type* F </code> 23 // the __c_file_type typedef usually boils down to stdio's FILE 24 </p></li><li class="listitem"><p><code class="code">ios_base::openmode M </code> 25 // same as all the other uses of openmode 26 </p></li><li class="listitem"><p><code class="code">int_type B </code> 27 // buffer size, defaults to BUFSIZ if not specified 28 </p></li></ul></div><p> 29 For those wanting to use file descriptors instead of FILE*'s, I 30 invite you to contemplate the mysteries of C's <code class="code">fdopen()</code>. 31 </p></li><li class="listitem"><p>In library snapshot 3.0.95 and later, <code class="code">filebuf</code>s bring 32 back an old extension: the <code class="code">fd()</code> member function. The 33 integer returned from this function can be used for whatever file 34 descriptors can be used for on your platform. Naturally, the 35 library cannot track what you do on your own with a file descriptor, 36 so if you perform any I/O directly, don't expect the library to be 37 aware of it. 38 </p></li><li class="listitem"><p>Beginning with 3.1, the extra <code class="code">filebuf</code> constructor and 39 the <code class="code">fd()</code> function were removed from the standard 40 filebuf. Instead, <code class="code"><ext/stdio_filebuf.h></code> contains 41 a derived class called 42 <a class="ulink" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00074.html" target="_top"><code class="code">__gnu_cxx::stdio_filebuf</code></a>. 43 This class can be constructed from a C <code class="code">FILE*</code> or a file 44 descriptor, and provides the <code class="code">fd()</code> function. 45 </p></li></ul></div><p>If you want to access a <code class="code">filebuf</code>'s file descriptor to 46 implement file locking (e.g. using the <code class="code">fcntl()</code> system 47 call) then you might be interested in Henry Suter's RWLock class. 48 49 </p><p> 50 </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_iterators.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ext_demangling.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 38. 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