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 .