STDIPC(3C-SVR4)     RISC/os Reference Manual      STDIPC(3C-SVR4)



NAME
     stdipc: ftok - standard interprocess communication package

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

     keyt ftok(const char *path, int id);

DESCRIPTION
     All interprocess communication facilities require the user
     to supply a key to be used by the msgget(2), semget(2), and
     shmget(2) system calls to obtain interprocess communication
     identifiers.  One suggested method for forming a key is to
     use the ftok subroutine described below.  Another way to
     compose keys is to include the project ID in the most signi-
     ficant byte and to use the remaining portion as a sequence
     number.  There are many other ways to form keys, but it is
     necessary for each system to define standards for forming
     them.  If some standard is not adhered to, it will be possi-
     ble for unrelated processes to unintentionally interfere
     with each other's operation.  It is still possible to inter-
     face intentionally.  Therefore, it is strongly suggested
     that the most significant byte of a key in some sense refer
     to a project so that keys do not conflict across a given
     system.

     ftok returns a key based on path and id that is usable in
     subsequent msgget, semget, and shmget system calls.  path
     must be the path name of an existing file that is accessible
     to the process.  id is a character that 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 when called with the same file name
     but different ids.

SEE ALSO
     intro(2), msgget(2), semget(2), shmget(2).

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

NOTES
     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.






                        Printed 11/19/92                   Page 1