PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       perror — write error messages to standard error

SYNOPSIS

       #include <stdio.h>

       void perror(const char *s);

DESCRIPTION

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2017 defers to the ISO C standard.

       The  perror()  function  shall  map  the  error  number  accessed through the symbol errno to a language-
       dependent error message, which shall be written to the standard error stream as follows:

        *  First (if s is not a null pointer and the character pointed to by s is not the null byte), the string
           pointed to by s followed by a <colon> and a <space>.

        *  Then an error message string followed by a <newline>.

       The contents of the error message strings shall be the same as those returned by strerror() with argument
       errno.

       The perror() function shall mark for update the last  data  modification  and  last  file  status  change
       timestamps  of  the  file  associated  with the standard error stream at some time between its successful
       completion and exit(), abort(), or the completion of fflush() or fclose() on stderr.

       The perror() function shall not change the orientation of the standard error stream.

       On error, perror() shall set the error indicator for the stream to which stderr  points,  and  shall  set
       errno to indicate the error.

       Since  no  value  is  returned,  an  application  wishing  to  check  for  error  situations  should call
       clearerr(stderr) before calling perror(), then if ferror(stderr) returns non-zero,  the  value  of  errno
       indicates which error occurred.

RETURN VALUE

       The perror() function shall not return a value.

ERRORS

       Refer to fputc().

       The following sections are informative.

EXAMPLES

   Printing an Error Message for a Function
       The  following  example replaces bufptr with a buffer that is the necessary size. If an error occurs, the
       perror() function prints a message and the program exits.

           #include <stdio.h>
           #include <stdlib.h>
           ...
           char *bufptr;
           size_t szbuf;
           ...
           if ((bufptr = malloc(szbuf)) == NULL) {
               perror("malloc"); exit(2);
           }
           ...

APPLICATION USAGE

       Application writers may prefer to use alternative interfaces instead of perror(), such as strerror_r() in
       combination with fprintf().

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       fprintf(), fputc(), psiginfo(), strerror()

       The Base Definitions volume of POSIX.1‐2017, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        PERROR(3POSIX)