stdipc(3C)           COMPATIBILITY FUNCTIONS           stdipc(3C)



NAME
     stdipc: ftok - standard interprocess communication package

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

     keyt ftok(const char *path, int 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.  It is still possible to inter-
     face intentionally.  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 path name of an existing file that is accessible
     to  the process.  id is a character that 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 (keyt) -1 if path does not exist or if  it  is
     not accessible to the process.

NOTES
     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.






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