ftok - convert a pathname and a project identifier to a Sys-
tem V IPC key
# include <sys/types.h>
# include <sys/ipc.h>
key_t ftok ( char *pathname, char proj )
The function converts the pathname of an existing accessible
file and a project identifier into a key_t type System V IPC
On success the return value will be the converted key_t
value, otherwise -1 with errno indicating the error as for
the stat(2) system call.
The generated key_t value is obtained stat-ing the disk file
corresponding to pathname in order to get its i-node number
and the minor device number of the filesystem on which the
disk file resides, then by combining the 8 bit proj value
along with the lower 16 bits of the i-node number, along
with the 8 bits of the minor device number. The algorithm
does not guarantee a unique key value. In fact
o Two different names linking to the same file produce
same key values.
o Using the lower 16 bits of the i-node number, gives
some chance (also usually small) to have same key
values for file names referring to different i-nodes.
o Not discriminating among major device numbers, gives
some chance of collision (also usually small) for sys-
tems with multiple disk controllers.
ipc(5), msgget(2), semget(2), shmget(2), stat(2).