| <html lang="en"> |
| <head> |
| <title>Exit Status - 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="Program-Termination.html#Program-Termination" title="Program Termination"> |
| <link rel="prev" href="Normal-Termination.html#Normal-Termination" title="Normal Termination"> |
| <link rel="next" href="Cleanups-on-Exit.html#Cleanups-on-Exit" title="Cleanups on Exit"> |
| <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="Exit-Status"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Cleanups-on-Exit.html#Cleanups-on-Exit">Cleanups on Exit</a>, |
| Previous: <a rel="previous" accesskey="p" href="Normal-Termination.html#Normal-Termination">Normal Termination</a>, |
| Up: <a rel="up" accesskey="u" href="Program-Termination.html#Program-Termination">Program Termination</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">25.6.2 Exit Status</h4> |
| |
| <p><a name="index-exit-status-3135"></a> |
| When a program exits, it can return to the parent process a small |
| amount of information about the cause of termination, using the |
| <dfn>exit status</dfn>. This is a value between 0 and 255 that the exiting |
| process passes as an argument to <code>exit</code>. |
| |
| <p>Normally you should use the exit status to report very broad information |
| about success or failure. You can't provide a lot of detail about the |
| reasons for the failure, and most parent processes would not want much |
| detail anyway. |
| |
| <p>There are conventions for what sorts of status values certain programs |
| should return. The most common convention is simply 0 for success and 1 |
| for failure. Programs that perform comparison use a different |
| convention: they use status 1 to indicate a mismatch, and status 2 to |
| indicate an inability to compare. Your program should follow an |
| existing convention if an existing convention makes sense for it. |
| |
| <p>A general convention reserves status values 128 and up for special |
| purposes. In particular, the value 128 is used to indicate failure to |
| execute another program in a subprocess. This convention is not |
| universally obeyed, but it is a good idea to follow it in your programs. |
| |
| <p><strong>Warning:</strong> Don't try to use the number of errors as the exit |
| status. This is actually not very useful; a parent process would |
| generally not care how many errors occurred. Worse than that, it does |
| not work, because the status value is truncated to eight bits. |
| Thus, if the program tried to report 256 errors, the parent would |
| receive a report of 0 errors—that is, success. |
| |
| <p>For the same reason, it does not work to use the value of <code>errno</code> |
| as the exit status—these can exceed 255. |
| |
| <p><strong>Portability note:</strong> Some non-POSIX systems use different |
| conventions for exit status values. For greater portability, you can |
| use the macros <code>EXIT_SUCCESS</code> and <code>EXIT_FAILURE</code> for the |
| conventional status value for success and failure, respectively. They |
| are declared in the file <samp><span class="file">stdlib.h</span></samp>. |
| <a name="index-stdlib_002eh-3136"></a> |
| <!-- stdlib.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Macro: int <b>EXIT_SUCCESS</b><var><a name="index-EXIT_005fSUCCESS-3137"></a></var><br> |
| <blockquote><p>This macro can be used with the <code>exit</code> function to indicate |
| successful program completion. |
| |
| <p>On POSIX systems, the value of this macro is <code>0</code>. On other |
| systems, the value might be some other (possibly non-constant) integer |
| expression. |
| </p></blockquote></div> |
| |
| <!-- stdlib.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>EXIT_FAILURE</b><var><a name="index-EXIT_005fFAILURE-3138"></a></var><br> |
| <blockquote><p>This macro can be used with the <code>exit</code> function to indicate |
| unsuccessful program completion in a general sense. |
| |
| <p>On POSIX systems, the value of this macro is <code>1</code>. On other |
| systems, the value might be some other (possibly non-constant) integer |
| expression. Other nonzero status values also indicate failures. Certain |
| programs use different nonzero status values to indicate particular |
| kinds of "non-success". For example, <code>diff</code> uses status value |
| <code>1</code> to mean that the files are different, and <code>2</code> or more to |
| mean that there was difficulty in opening the files. |
| </p></blockquote></div> |
| |
| <p>Don't confuse a program's exit status with a process' termination status. |
| There are lots of ways a process can terminate besides having it's program |
| finish. In the event that the process termination <em>is</em> caused by program |
| termination (i.e., <code>exit</code>), though, the program's exit status becomes |
| part of the process' termination status. |
| |
| </body></html> |
| |
