229 lines
5.0 KiB
HTML
229 lines
5.0 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of PERROR</TITLE>
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</HEAD><BODY>
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<H1>PERROR</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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perror - print a system error message
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/stdio.h">stdio.h</A>></B>
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<P>
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<B>void perror(const char *</B><I>s</I><B>);</B>
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<P>
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<B>#include <<A HREF="file:///usr/include/errno.h">errno.h</A>></B>
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<P>
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<B>const char * const </B><I>sys_errlist</I><B>[];</B>
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<BR>
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<B>int </B><I>sys_nerr</I><B>;</B>
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<BR>
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<B>int </B><I>errno</I><B>; </B>/* Not really declared this way; see <A HREF="/cgi-bin/man/man2html?3+errno">errno</A>(3) */
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<I>sys_errlist</I>,
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<I>sys_nerr</I>:
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<BR> Since glibc 2.19:
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<BR> _DEFAULT_SOURCE
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<BR> Glibc 2.19 and earlier:
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<BR> _BSD_SOURCE
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>perror</B>()
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function produces a message on standard error describing the last
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error encountered during a call to a system or library function.
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<P>
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First (if
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<I>s</I>
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is not NULL and
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<I>*s</I>
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is not a null byte ('\0')), the argument string
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<I>s</I>
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is printed, followed by a colon and a blank.
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Then an error message corresponding to the current value of
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<I>errno</I>
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and a new-line.
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<P>
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To be of most use, the argument string should include the name
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of the function that incurred the error.
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<P>
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The global error list
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<I>sys_errlist</I>[],
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which can be indexed by
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<I>errno</I>,
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can be used to obtain the error message without the newline.
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The largest message number provided in the table is
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<I>sys_nerr</I>-1.
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Be careful when directly accessing this list, because new error values
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may not have been added to
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<I>sys_errlist</I>[].
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The use of
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<I>sys_errlist</I>[]
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is nowadays deprecated; use
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<B><A HREF="/cgi-bin/man/man2html?3+strerror">strerror</A></B>(3)
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instead.
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<P>
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When a system call fails, it usually returns -1 and sets the
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variable
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<I>errno</I>
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to a value describing what went wrong.
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(These values can be found in
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<I><<A HREF="file:///usr/include/errno.h">errno.h</A>></I>.)
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Many library functions do likewise.
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The function
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<B>perror</B>()
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serves to translate this error code into human-readable form.
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Note that
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<I>errno</I>
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is undefined after a successful system call or library function call:
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this call may well change this variable, even though it succeeds,
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for example because it internally used some other library function that failed.
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Thus, if a failing call is not immediately followed by a call to
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<B>perror</B>(),
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the value of
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<I>errno</I>
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should be saved.
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<A NAME="lbAE"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>perror</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe race:stderr<BR></TD></TR>
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</TABLE>
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<P>
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<A NAME="lbAF"> </A>
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<H2>CONFORMING TO</H2>
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<B>perror</B>(),
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<I>errno</I>:
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POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD.
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<P>
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The externals
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<I>sys_nerr</I>
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and
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<I>sys_errlist</I>
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derive from BSD, but are not specified in POSIX.1.
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<A NAME="lbAG"> </A>
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<H2>NOTES</H2>
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The externals
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<I>sys_nerr</I>
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and
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<I>sys_errlist</I>
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are defined by glibc, but in
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<I><<A HREF="file:///usr/include/stdio.h">stdio.h</A>></I>.
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<A NAME="lbAH"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+err">err</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+errno">errno</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+error">error</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strerror">strerror</A></B>(3)
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<A NAME="lbAI"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">ATTRIBUTES</A><DD>
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<DT id="5"><A HREF="#lbAF">CONFORMING TO</A><DD>
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<DT id="6"><A HREF="#lbAG">NOTES</A><DD>
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<DT id="7"><A HREF="#lbAH">SEE ALSO</A><DD>
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<DT id="8"><A HREF="#lbAI">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:52 GMT, March 31, 2021
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</BODY>
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</HTML>
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