stdipc(3c)                 DG/UX 4.30                  stdipc(3c)



     NAME
          ftok - standard interprocess communication package

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

          keyt ftok(path, id)
          char *path;
          char 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 way to form a key is to use the ftok
          subroutine described below.  Another way is to include the
          project ID in the most significant byte and to use the
          remaining bytes as a sequence number.

          There are many other ways to form keys; each system must
          define standards for forming them.  If some standard is not
          adhered to, unrelated processes might interfere with each
          other's operation.  Therefore, the most significant byte of
          a key should in some sense refer to a project so that keys
          do not conflict.

          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 filename but
          different ids.

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

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

     WARNING
          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 will likely return a key different from
          the one it returned the first time it was called.






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