| <html lang="en"> |
| <head> |
| <title>Standard Streams - 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="I_002fO-on-Streams.html#I_002fO-on-Streams" title="I/O on Streams"> |
| <link rel="prev" href="Streams.html#Streams" title="Streams"> |
| <link rel="next" href="Opening-Streams.html#Opening-Streams" title="Opening Streams"> |
| <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="Standard-Streams"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Opening-Streams.html#Opening-Streams">Opening Streams</a>, |
| Previous: <a rel="previous" accesskey="p" href="Streams.html#Streams">Streams</a>, |
| Up: <a rel="up" accesskey="u" href="I_002fO-on-Streams.html#I_002fO-on-Streams">I/O on Streams</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">12.2 Standard Streams</h3> |
| |
| <p><a name="index-standard-streams-918"></a><a name="index-streams_002c-standard-919"></a> |
| When the <code>main</code> function of your program is invoked, it already has |
| three predefined streams open and available for use. These represent |
| the “standard” input and output channels that have been established |
| for the process. |
| |
| <p>These streams are declared in the header file <samp><span class="file">stdio.h</span></samp>. |
| <a name="index-stdio_002eh-920"></a> |
| <!-- stdio.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Variable: FILE * <b>stdin</b><var><a name="index-stdin-921"></a></var><br> |
| <blockquote><p>The <dfn>standard input</dfn> stream, which is the normal source of input for the |
| program. |
| </p></blockquote></div> |
| <a name="index-standard-input-stream-922"></a> |
| <!-- stdio.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Variable: FILE * <b>stdout</b><var><a name="index-stdout-923"></a></var><br> |
| <blockquote><p>The <dfn>standard output</dfn> stream, which is used for normal output from |
| the program. |
| </p></blockquote></div> |
| <a name="index-standard-output-stream-924"></a> |
| <!-- stdio.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Variable: FILE * <b>stderr</b><var><a name="index-stderr-925"></a></var><br> |
| <blockquote><p>The <dfn>standard error</dfn> stream, which is used for error messages and |
| diagnostics issued by the program. |
| </p></blockquote></div> |
| <a name="index-standard-error-stream-926"></a> |
| In the GNU system, you can specify what files or processes correspond to |
| these streams using the pipe and redirection facilities provided by the |
| shell. (The primitives shells use to implement these facilities are |
| described in <a href="File-System-Interface.html#File-System-Interface">File System Interface</a>.) Most other operating systems |
| provide similar mechanisms, but the details of how to use them can vary. |
| |
| <p>In the GNU C library, <code>stdin</code>, <code>stdout</code>, and <code>stderr</code> are |
| normal variables which you can set just like any others. For example, |
| to redirect the standard output to a file, you could do: |
| |
| <pre class="smallexample"> fclose (stdout); |
| stdout = fopen ("standard-output-file", "w"); |
| </pre> |
| <p>Note however, that in other systems <code>stdin</code>, <code>stdout</code>, and |
| <code>stderr</code> are macros that you cannot assign to in the normal way. |
| But you can use <code>freopen</code> to get the effect of closing one and |
| reopening it. See <a href="Opening-Streams.html#Opening-Streams">Opening Streams</a>. |
| |
| <p>The three streams <code>stdin</code>, <code>stdout</code>, and <code>stderr</code> are not |
| unoriented at program start (see <a href="Streams-and-I18N.html#Streams-and-I18N">Streams and I18N</a>). |
| |
| </body></html> |
| |
