.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "PERROR" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" perror 
.SH 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.
.SH NAME
perror \- write error messages to standard error
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
.sp
void perror(const char *\fP\fIs\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIperror\fP() function shall map the error number accessed through
the symbol \fIerrno\fP to a language-dependent error
message, which shall be written to the standard error stream as follows:
.IP " *" 3
First (if \fIs\fP is not a null pointer and the character pointed
to by \fIs\fP is not the null byte), the string pointed to
by \fIs\fP followed by a colon and a <space>.
.LP
.IP " *" 3
Then an error message string followed by a <newline>.
.LP
.LP
The contents of the error message strings shall be the same as those
returned by \fIstrerror\fP() with argument \fIerrno\fP.
.LP
The
\fIperror\fP() function shall mark the file associated with the standard
error stream as having been written (\fIst_ctime\fP,
\fIst_mtime\fP marked for update) at some time between its successful
completion and \fIexit\fP(), \fIabort\fP(), or the completion of \fIfflush\fP()
or \fIfclose\fP() on \fIstderr\fP. 
.LP
The \fIperror\fP() function shall not change the orientation of the
standard error stream.
.SH RETURN VALUE
.LP
The \fIperror\fP() function shall not return a value.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Printing an Error Message for a Function
.LP
The following example replaces \fIbufptr\fP with a buffer that is
the necessary size. If an error occurs, the \fIperror\fP()
function prints a message and the program exits.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <stdlib.h>
\&...
char *bufptr;
size_t szbuf;
\&...
if ((bufptr = malloc(szbuf)) == NULL) {
    perror("malloc"); exit(2);
}
\&...
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIstrerror\fP(), the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<stdio.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .