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FTOK
Section: Linux Programmer's Manual (3)Updated: 2001-11-28
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NAME
ftok - convert a pathname and a project identifier to a System V IPC keySYNOPSIS
# include <sys/types.h> # include <sys/ipc.h>
key_t ftok(const char *pathname, int proj_id);
DESCRIPTION
The ftok function uses the identity of the file named by the given pathname (which must refer to an existing, accessible file) and the least significant 8 bits of proj_id (which must be nonzero) to generate a key_t type System V IPC key, suitable for use with msgget(2), semget(2), or shmget(2).The resulting value is the same for all pathnames that name the same file, when the same value of proj_id is used. The value returned should be different when the (simultaneously existing) files or the project IDs differ.
RETURN VALUE
On success the generated key_t value is returned. On failure -1 is returned, with errno indicating the error as for the stat(2) system call.CONFORMING TO
XPG4NOTES
Under libc4 and libc5 (and under SunOS 4.x) the prototype was- key_t ftok(char *pathname, char proj_id);
Of course no guarantee can be given that the resulting key_t is unique. Typically, a best effort attempt combines the given proj_id byte, the lower 16 bits of the i-node number, and the lower 8 bits of the device number into a 32-bit result. Collisions may easily happen, for example between files on /dev/hda1 and files on /dev/sda1.
SEE ALSO
ipc(5), msgget(2), semget(2), shmget(2), stat(2)