| <html lang="en"> |
| <head> |
| <title>Linked Channels - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Stream_002fDescriptor-Precautions.html#Stream_002fDescriptor-Precautions" title="Stream/Descriptor Precautions"> |
| <link rel="next" href="Independent-Channels.html#Independent-Channels" title="Independent Channels"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Linked-Channels"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Independent-Channels.html#Independent-Channels">Independent Channels</a>, |
| Up: <a rel="up" accesskey="u" href="Stream_002fDescriptor-Precautions.html#Stream_002fDescriptor-Precautions">Stream/Descriptor Precautions</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">13.5.1 Linked Channels</h4> |
| |
| <p><a name="index-linked-channels-1246"></a> |
| Channels that come from a single opening share the same file position; |
| we call them <dfn>linked</dfn> channels. Linked channels result when you |
| make a stream from a descriptor using <code>fdopen</code>, when you get a |
| descriptor from a stream with <code>fileno</code>, when you copy a descriptor |
| with <code>dup</code> or <code>dup2</code>, and when descriptors are inherited |
| during <code>fork</code>. For files that don't support random access, such as |
| terminals and pipes, <em>all</em> channels are effectively linked. On |
| random-access files, all append-type output streams are effectively |
| linked to each other. |
| |
| <p><a name="index-cleaning-up-a-stream-1247"></a>If you have been using a stream for I/O (or have just opened the stream), |
| and you want to do I/O using |
| another channel (either a stream or a descriptor) that is linked to it, |
| you must first <dfn>clean up</dfn> the stream that you have been using. |
| See <a href="Cleaning-Streams.html#Cleaning-Streams">Cleaning Streams</a>. |
| |
| <p>Terminating a process, or executing a new program in the process, |
| destroys all the streams in the process. If descriptors linked to these |
| streams persist in other processes, their file positions become |
| undefined as a result. To prevent this, you must clean up the streams |
| before destroying them. |
| |
| </body></html> |
| |
