.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FTOK" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" ftok 
.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
ftok \- generate an IPC key
.SH SYNOPSIS
.LP
\fB#include <sys/ipc.h>
.br
.sp
key_t ftok(const char *\fP\fIpath\fP\fB, int\fP \fIid\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIftok\fP() function shall return a key based on \fIpath\fP and
\fIid\fP that is usable in subsequent calls to \fImsgget\fP(), \fIsemget\fP(),
and \fIshmget\fP(). The application shall ensure that the \fIpath\fP
argument is the pathname of an
existing file that the process is able to \fIstat\fP().
.LP
The \fIftok\fP() function shall return the same key value for all
paths that name the same file, when called with the same
\fIid\fP value, and return different key values when called with different
\fIid\fP values or with paths that name different
files existing on the same file system at the same time. It is unspecified
whether \fIftok\fP() shall return the same key value
when called again after the file named by \fIpath\fP is removed and
recreated with the same name.
.LP
Only the low-order 8-bits of \fIid\fP are significant. The behavior
of \fIftok\fP() is unspecified if these bits are 0.
.SH RETURN VALUE
.LP
Upon successful completion, \fIftok\fP() shall return a key. Otherwise,
\fIftok\fP() shall return (\fBkey_t\fP)-1 and set
\fIerrno\fP to indicate the error.
.SH ERRORS
.LP
The \fIftok\fP() function shall fail if:
.TP 7
.B EACCES
Search permission is denied for a component of the path prefix.
.TP 7
.B ELOOP
A loop exists in symbolic links encountered during resolution of the
\fIpath\fP argument.
.TP 7
.B ENAMETOOLONG
The length of the \fIpath\fP argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
.TP 7
.B ENOENT
A component of \fIpath\fP does not name an existing file or \fIpath\fP
is an empty string.
.TP 7
.B ENOTDIR
A component of the path prefix is not a directory.
.sp
.LP
The \fIftok\fP() function may fail if:
.TP 7
.B ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the \fIpath\fP argument.
.TP 7
.B ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result
whose length exceeds {PATH_MAX}.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Getting an IPC Key
.LP
The following example gets a unique key that can be used by the IPC
functions \fIsemget\fP(), \fImsgget\fP(), and \fIshmget\fP(). The
key returned by \fIftok\fP() for this example is based on the ID value
\fIS\fP and the pathname \fB/tmp\fP.
.sp
.RS
.nf

\fB#include <sys/ipc.h>
\&...
key_t key;
char *path = "/tmp";
int id = 'S';
.sp

key = ftok(path, id);
\fP
.fi
.RE
.SS Saving an IPC Key
.LP
The following example gets a unique key based on the pathname \fB/tmp\fP
and the ID value \fIa\fP. It also assigns the value
of the resulting key to the \fIsemkey\fP variable so that it will
be available to a later call to \fIsemget\fP(), \fImsgget\fP(), or
\fIshmget\fP().
.sp
.RS
.nf

\fB#include <sys/ipc.h>
\&...
key_t semkey;
.sp

if ((semkey = ftok("/tmp", 'a')) == (key_t) -1) {
    perror("IPC error: ftok"); exit(1);
}
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
For maximum portability, \fIid\fP should be a single-byte character.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fImsgget\fP(), \fIsemget\fP(), \fIshmget\fP(), the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, \fI<sys/ipc.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 .