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 *sys_errlist[];
       int sys_nerr;
       int errno;

   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 message 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[].

       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 functions 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 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                                           2007-07-26                                                  PERROR(3)