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+<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 38. Input and Output</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="extensions.html" title="Part XII. Extensions" /><link rel="prev" href="ext_iterators.html" title="Chapter 37. Iterators" /><link rel="next" href="ext_demangling.html" title="Chapter 39. Demangling" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 38. 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.
+ Extensions
+
+</th><td width="20%" align="right"> <a accesskey="n" href="ext_demangling.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.io"></a>Chapter 38. 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>
+ Extensions allowing <code class="code">filebuf</code>s to be constructed from
+ "C" types like FILE*s and file descriptors.
+ </p><div class="sect1" lang="en" xml:lang="en"><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
+ <code class="code">std::filebuf</code>s from C stdio types such as
+ <code class="code">FILE*</code>s and POSIX file descriptors.
+ Today the recommended way to use stdio types with libstdc++
+ IOStreams is via the <code class="code">stdio_filebuf</code> class (see below),
+ but earlier releases provided slightly different mechanisms.
+ </p><div class="itemizedlist"><ul type="disc"><li><p>3.0.x <code class="code">filebuf</code>s have another ctor with this signature:
+ <code class="code">basic_filebuf(__c_file_type*, ios_base::openmode, int_type);
+ </code>
+ This comes in very handy in a number of places, such as
+ attaching Unix sockets, pipes, and anything else which uses file
+ descriptors, into the IOStream buffering classes. The three
+ arguments are as follows:
+ </p><div class="itemizedlist"><ul type="circle"><li><p><code class="code">__c_file_type* F </code>
+ // the __c_file_type typedef usually boils down to stdio's FILE
+ </p></li><li><p><code class="code">ios_base::openmode M </code>
+ // same as all the other uses of openmode
+ </p></li><li><p><code class="code">int_type B </code>
+ // buffer size, defaults to BUFSIZ if not specified
+ </p></li></ul></div><p>
+ For those wanting to use file descriptors instead of FILE*'s, I
+ invite you to contemplate the mysteries of C's <code class="code">fdopen()</code>.
+ </p></li><li><p>In library snapshot 3.0.95 and later, <code class="code">filebuf</code>s bring
+ back an old extension: the <code class="code">fd()</code> member function. The
+ integer returned from this function can be used for whatever file
+ descriptors can be used for on your platform. Naturally, the
+ library cannot track what you do on your own with a file descriptor,
+ so if you perform any I/O directly, don't expect the library to be
+ aware of it.
+ </p></li><li><p>Beginning with 3.1, the extra <code class="code">filebuf</code> constructor and
+ the <code class="code">fd()</code> function were removed from the standard
+ filebuf. Instead, <code class="code"><ext/stdio_filebuf.h></code> contains
+ a derived class called
+ <a class="ulink" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/class____gnu__cxx_1_1stdio__filebuf.html" target="_top"><code class="code">__gnu_cxx::stdio_filebuf</code></a>.
+ This class can be constructed from a C <code class="code">FILE*</code> or a file
+ descriptor, and provides the <code class="code">fd()</code> function.
+ </p></li></ul></div><p>If you want to access a <code class="code">filebuf</code>'s file descriptor to
+ implement file locking (e.g. using the <code class="code">fcntl()</code> system
+ call) then you might be interested in Henry Suter's
+ <a class="ulink" href="http://suter.home.cern.ch/suter/RWLock.html" target="_top">RWLock</a>
+ class.
+ </p><p>
+ </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 37. Iterators </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 39. Demangling</td></tr></table></div></body></html>
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