stdipc(3C)                                                stdipc(3C)


       NAME
             stdipc: ftok - standard interprocess communication package

       SYNOPSIS
             #include <sys/types.h>
             #include <sys/ipc.h>
             key_t 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 significant 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 possible for unrelated processes
             to unintentionally interfere with each other's operation.  It
             is still possible to interface 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.

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

       REFERENCES
             intro(2), msgget(2), semget(2), shmget(2)

       NOTICES
             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


                           Copyright 1994 Novell, Inc.               Page 1

      stdipc(3C)                                                stdipc(3C)


            it did the original time it was called.















































                          Copyright 1994 Novell, Inc.               Page 2