PERROR(3)                           Linux Programmer's Manual                           PERROR(3)



NAME
       perror - print a system error message

SYNOPSIS
       #include <stdio.h>

       void perror(const char *s);

       #include <errno.h>

       const char * const sys_errlist[];
       int sys_nerr;
       int errno; /* Not really declared this way; see errno(3). */

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sys_errlist, sys_nerr: _BSD_SOURCE

DESCRIPTION
       The  routine perror() produces a message on the standard error output, describing the last
       error encountered during a call to a system or library function.  First (if s is not  NULL
       and  *s  is  not a null byte ('\0')) the argument string s is printed, followed by a colon
       and a blank.  Then the message and a new-line.

       To be of most use, the argument string should  include  the  name  of  the  function  that
       incurred  the error.  The error number is taken from the external variable errno, which is
       set when errors occur but not cleared when successful calls are made.

       The global error list sys_errlist[] indexed by errno can be used to obtain the error  mes‐
       sage without the newline.  The largest message number provided in the table is sys_nerr-1.
       Be careful when directly accessing this list because new error values may  not  have  been
       added to sys_errlist[].  The use of sys_errlist[] is nowadays deprecated.

       When  a  system  call  fails, it usually returns -1 and sets the variable errno to a value
       describing what went wrong.  (These values can be found in <errno.h>.)  Many library func‐
       tions  do likewise.  The function perror() serves to translate this error code into human-
       readable form.  Note that errno is undefined after a successful library  call:  this  call
       may  well change this variable, even though it succeeds, for example because it internally
       used some other library function that failed.  Thus, if a failing call is not  immediately
       followed by a call to perror(), the value of errno should be saved.

CONFORMING TO
       The  function  perror() and the external errno (see errno(3)) conform to C89, C99, 4.3BSD,
       POSIX.1-2001.  The externals sys_nerr and sys_errlist conform to BSD.

NOTES
       The externals sys_nerr and sys_errlist are defined by glibc, but in <stdio.h>.

SEE ALSO
       err(3), errno(3), error(3), strerror(3)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



                                            2014-05-28                                  PERROR(3)