ftok(3C)                                                 ftok(3C)



NAME
     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 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.

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

WARNINGS
     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.

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







January 1992                                                    1