stdipc(3C)                                             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 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 a
          standard is not adhered to, unrelated processes may
          interfere with each other's operation.  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 pathname of an existing file that is accessible
          to the process.  id is a character that uniquely identifies
          a project.  ftok returns the same key for linked files when
          called with the same id; it returns 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, ftok is likely to return a different key than it
          did the original time it was called.







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