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

       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.

       perror — write error messages to standard error

       #include <stdio.h>

       void perror(const char *s);

       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.1‐2008 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

       The perror() function shall not return a value.

       Refer to fputc().

       The following sections are informative.

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



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

       The Base Definitions volume of POSIX.1‐2008, <stdio.h>

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical
       and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008
       with the 2013 Technical Corrigendum 1 applied.) 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 .

       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 .

IEEE/The Open Group                   2013                        PERROR(3POSIX)