ultrix man page for ftok

ftok(3) 						     Library Functions Manual							   ftok(3)

Name
       ftok - standard interprocess communication package

Syntax
       #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 and system calls to obtain interprocess commu-
       nication identifiers.  One suggested method for forming a key is to use the file to key, subroutine described below.  Another way  to  com-
       pose  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.  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.

       The subroutine returns a key based on path and id that is usable in subsequent and system calls.  The path must be  the	path  name  of	an
       existing  file  that  is  accessible to the process.  The id is a character which uniquely identifies a project.  Note that 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  dif-
       ferent ids.

Return Values
       The subroutine 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 is removed when keys still refer to the file, future calls to with the same path and id will return an
       error.  If the same file is recreated, then 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)

																	   ftok(3)