STDIPC(3C)           INTERACTIVE UNIX System           STDIPC(3C)



          NAME
               stdipc: ftok - standard interprocess communication package

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

               key_t 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 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.  Therefore, it is strongly sug-
               gested 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 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 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.

          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 is likely to return a different key
               than it did the original time it was called.





          Rev. C Software Development Set                            Page 1