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

PROLOG         top

       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         top

       perror — write error messages to standard error

SYNOPSIS         top

       #include <stdio.h>

       void perror(const char *s);

DESCRIPTION         top

       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 occurred.

RETURN VALUE         top

       The perror() function shall not return a value.

ERRORS         top

       Refer to fputc(3p).

       The following sections are informative.

EXAMPLES         top

   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().

RATIONALE         top




SEE ALSO         top

       fprintf(3p), fputc(3p), psiginfo(3p), strerror(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       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(3P)