|FTOK(3)||Linux Programmer's Manual||FTOK(3)|
#include <sys/types.h> #include <sys/ipc.h>
key_t ftok(const char *pathname, int proj_id);
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.
|ftok ()||Thread safety||MT-Safe|
key_t ftok(char *pathname, char proj_id);
Today, proj_id is an int, but still only 8 bits are used. Typical usage has an ASCII character proj_id, that is why the behavior is said to be undefined when proj_id is zero.
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 inode 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.