ftok man page on Ultrix

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ftok(3)								       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  communi‐
       cation  identifiers.   One suggested method for forming a key is to use
       the file to key, 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 stan‐
       dards 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 different
       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 dif‐
       ferent key than it did the original time it was called.

See Also
       intro(2), msgget(2), semget(2), shmget(2)

								       ftok(3)
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