STDIPC(3C)               DOMAIN/IX SYS5                STDIPC(3C)



NAME
     ftok - interprocess communication package

USAGE
     #include <sys/types.h>
     #include <sys/ipc.h>

     key_t ftok(path, id)
     char *path;
     char id;


DESCRIPTION
     All of the System V interprocess communication facilities
     require the user to supply a key for the msgget(2),
     semget(2), and shmget(2) system calls to use when obtaining
     interprocess communication identifiers.  One method for
     forming a key is to use the ftok subroutine.

     Ftok returns a key based on path and id that is useable in
     subsequent msgget, semget, and shmget system calls.  Path
     must be the pathname of an existing file that is accessible
     to the process.  Id is a character which uniquely identifies
     a project.  Note that ftok will return the same key for
     linked files when called with the same id and that it will
     return different keys if you call it with the same filename
     but different ids.

NOTES
     Another way to compose keys is to include the project ID in
     the most significant byte and to use the remaining portion
     as a sequence number.  There are other ways to form keys,
     but unless a standard for forming them is established, it
     will be possible for unrelated processes to interfere, unin-
     tentionally, with each other's operation.  Therefore, making
     the most significant byte of a key refer, in some way, to a
     project will ensure that keys do not conflict across a given
     system.

     If the file whose path is passed to ftok is removed when
     keys still refer to the file, future calls to ftok with the
     same path and id will return an error.  If the same file is
     recreated, then ftok is likely to return a different key
     than it did the original time it was called.

DIAGNOSTICS
     Ftok returns (key_t) -1 if path does not exist or is not
     accessible to the process.





Printed 12/4/86                                          STDIPC-1

STDIPC(3C)               DOMAIN/IX SYS5                STDIPC(3C)



RELATED INFORMATION
     msgget(2), semget(2), shmget(2)



















































STDIPC-2                                          Printed 12/4/86