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3 <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 26. 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 III. Extensions" /><link rel="prev" href="ext_iterators.html" title="Chapter 25. Iterators" /><link rel="next" href="ext_demangling.html" title="Chapter 27. Demangling" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 26. 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 III.
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 26. Input and Output"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.io"></a>Chapter 26. 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);
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
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.
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