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



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

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 aa 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(3)
