stdipc(3)                           CLIX                           stdipc(3)



  NAME

    stdipc: ftok - A standard interprocess communication package

  LIBRARY

    Standard C Library (libc.a)

  SYNOPSIS

    #include <sys/types.h>

    #include <sys/ipc.h>

    key_t ftok(
      char *path ,
      char id );

  PARAMETERS

    path   The pathname of an existing file that is accessible to the process.

    id     A character that uniquely identifies a project.

  DESCRIPTION

    All interprocess communication facilities require the user to supply a key
    to be used by the msgget(), semget(), and shmget() functions to obtain
    interprocess communication identifiers.  One suggested method for forming
    a key is to use the ftok() function 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 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 ftok() function returns a key based on path and id that is usable in
    subsequent msgget(), semget(), and shmget() functions.  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 filename but
    different ids.

  CAUTIONS

    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 previous time it was called.



  2/94 - Intergraph Corporation                                              1

  stdipc(3)                           CLIX                           stdipc(3)



  RETURN VALUES

    The ftok() function returns (key_t) -1 if path does not exist or if it is
    not accessible to the process.

  RELATED INFORMATION

    Functions: msgget(2), semget(2), shmget(2), intro(2)














































  2                                              Intergraph Corporation - 2/94