| <html lang="en"> |
| <head> |
| <title>Error Recovery - 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="EOF-and-Errors.html#EOF-and-Errors" title="EOF and Errors"> |
| <link rel="next" href="Binary-Streams.html#Binary-Streams" title="Binary 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="Error-Recovery"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Binary-Streams.html#Binary-Streams">Binary Streams</a>, |
| Previous: <a rel="previous" accesskey="p" href="EOF-and-Errors.html#EOF-and-Errors">EOF and Errors</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">12.16 Recovering from errors</h3> |
| |
| <p>You may explicitly clear the error and EOF flags with the <code>clearerr</code> |
| function. |
| |
| <!-- stdio.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: void <b>clearerr</b> (<var>FILE *stream</var>)<var><a name="index-clearerr-1102"></a></var><br> |
| <blockquote><p>This function clears the end-of-file and error indicators for the |
| stream <var>stream</var>. |
| |
| <p>The file positioning functions (see <a href="File-Positioning.html#File-Positioning">File Positioning</a>) also clear the |
| end-of-file indicator for the stream. |
| </p></blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: void <b>clearerr_unlocked</b> (<var>FILE *stream</var>)<var><a name="index-clearerr_005funlocked-1103"></a></var><br> |
| <blockquote><p>The <code>clearerr_unlocked</code> function is equivalent to the <code>clearerr</code> |
| function except that it does not implicitly lock the stream. |
| |
| <p>This function is a GNU extension. |
| </p></blockquote></div> |
| |
| <p>Note that it is <em>not</em> correct to just clear the error flag and retry |
| a failed stream operation. After a failed write, any number of |
| characters since the last buffer flush may have been committed to the |
| file, while some buffered data may have been discarded. Merely retrying |
| can thus cause lost or repeated data. |
| |
| <p>A failed read may leave the file pointer in an inappropriate position for |
| a second try. In both cases, you should seek to a known position before |
| retrying. |
| |
| <p>Most errors that can happen are not recoverable — a second try will |
| always fail again in the same way. So usually it is best to give up and |
| report the error to the user, rather than install complicated recovery |
| logic. |
| |
| <p>One important exception is <code>EINTR</code> (see <a href="Interrupted-Primitives.html#Interrupted-Primitives">Interrupted Primitives</a>). |
| Many stream I/O implementations will treat it as an ordinary error, which |
| can be quite inconvenient. You can avoid this hassle by installing all |
| signals with the <code>SA_RESTART</code> flag. |
| |
| <p>For similar reasons, setting nonblocking I/O on a stream's file |
| descriptor is not usually advisable. |
| |
| </body></html> |
| |
