| <?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>Chapter 27. Input and Output</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="extensions.html" title="Part III. Extensions" /><link rel="prev" href="ext_iterators.html" title="Chapter 26. Iterators" /><link rel="next" href="ext_demangling.html" title="Chapter 28. Demangling" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 27. 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. |
| Extensions |
| |
| </th><td width="20%" align="right"> <a accesskey="n" href="ext_demangling.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.io"></a>Chapter 27. Input and Output</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><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="section"><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 class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><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 class="itemizedlist" style="list-style-type: circle; "><li class="listitem"><p><code class="code">__c_file_type* F </code> |
| // the __c_file_type typedef usually boils down to stdio's FILE |
| </p></li><li class="listitem"><p><code class="code">ios_base::openmode M </code> |
| // same as all the other uses of openmode |
| </p></li><li class="listitem"><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 class="listitem"><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 class="listitem"><p>Beginning with 3.1, the extra |
| <code class="classname">basic_filebuf</code> constructor and |
| the <code class="code">fd()</code> function were removed from the standard |
| filebuf. Instead, |
| <code class="filename"><ext/stdio_filebuf.h></code> |
| contains a derived class template called |
| <code class="classname">__gnu_cxx::stdio_filebuf</code>. |
| 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></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 26. Iterators </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 28. Demangling</td></tr></table></div></body></html> |
