NAME
ftok —
create IPC identifier from path
name
LIBRARY
library “libc”
SYNOPSIS
#include
<sys/types.h>
#include <sys/ipc.h>
key_t
ftok(const
char *path, int
id);
DESCRIPTION
Theftok()
function attempts to create a unique key suitable for use with the
msgget(2),
semget(2) and
shmget(2) functions given the path of an existing
file and a user-selectable id.
The specified path must specify an existing file that is accessible to the calling process or the call will fail. Also, note that links to files will return the same key, given the same id.
Only the 8 least significant bits of id are used in the key generation; the rest of the bits are ignored.
RETURN VALUES
The ftok() function will return
((key_t)-1) if path does not exist or if it cannot be
accessed by the calling process.
SEE ALSO
STANDARDS
The ftok() function conforms to
IEEE Std 1003.1 (“POSIX.1”).
HISTORY
The ftok() function originated with System
V and is typically used by programs that use the System V IPC routines.
AUTHORS
Thorsten Lockert <tholo@sigmasoft.com>
BUGS
The returned key is computed based on the device and inode of the specified path in combination with the given id. Thus it is quite possible for the routine to return duplicate keys given that those fields are not 8- and 16-bit quantities like they were on System V based systems where this library routine's ancestor were originally created.