# 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.