NAME
ftok —
create IPC identifier from path
name
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
key_t
ftok(
const char
*path,
int id);
DESCRIPTION
The
ftok() 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
msgget(2),
semget(2),
shmget(2)
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.