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  15     Extensions allowing <code class="code">filebuf</code>s to be constructed from
  16     "C" types like  FILE*s and file descriptors.
  17   </p><div class="section" title="Derived filebufs"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manual.ext.io.filebuf_derived"></a>Derived filebufs</h2></div></div></div><p>The v2 library included non-standard extensions to construct
  18       <code class="code">std::filebuf</code>s from C stdio types such as
  19       <code class="code">FILE*</code>s and POSIX file descriptors.
  20       Today the recommended way to use stdio types with libstdc++
  21       IOStreams is via the <code class="code">stdio_filebuf</code> class (see below),
  22       but earlier releases provided slightly different mechanisms.
  23    </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:
  24         <code class="code">basic_filebuf(__c_file_type*, ios_base::openmode, int_type);
  25         </code>
  26          This comes in very handy in a number of places, such as
  27          attaching Unix sockets, pipes, and anything else which uses file
  28          descriptors, into the IOStream buffering classes.  The three
  29          arguments are as follows:
  30          </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p><code class="code">__c_file_type*      F   </code>
  31               // the __c_file_type typedef usually boils down to stdio's FILE
  32           </p></li><li class="listitem"><p><code class="code">ios_base::openmode  M   </code>
  33               // same as all the other uses of openmode
  34           </p></li><li class="listitem"><p><code class="code">int_type            B   </code>
  35               // buffer size, defaults to BUFSIZ if not specified
  36           </p></li></ul></div><p>
  37          For those wanting to use file descriptors instead of FILE*'s, I
  38          invite you to contemplate the mysteries of C's <code class="code">fdopen()</code>.
  39      </p></li><li class="listitem"><p>In library snapshot 3.0.95 and later, <code class="code">filebuf</code>s bring
  40          back an old extension:  the <code class="code">fd()</code> member function.  The
  41          integer returned from this function can be used for whatever file
  42          descriptors can be used for on your platform.  Naturally, the
  43          library cannot track what you do on your own with a file descriptor,
  44          so if you perform any I/O directly, don't expect the library to be
  45          aware of it.
  46      </p></li><li class="listitem"><p>Beginning with 3.1, the extra <code class="code">filebuf</code> constructor and
  47          the <code class="code">fd()</code> function were removed from the standard
  48          filebuf.  Instead, <code class="code">&lt;ext/stdio_filebuf.h&gt;</code> contains
  49          a derived class called
  50          <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00074.html" target="_top"><code class="code">__gnu_cxx::stdio_filebuf</code></a>.
  51          This class can be constructed from a C <code class="code">FILE*</code> or a file
  52          descriptor, and provides the <code class="code">fd()</code> function.
  53      </p></li></ul></div></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 27. Iterators </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 29. Demangling</td></tr></table></div></body></html>