ftok(S)                        6 January 1993                        ftok(S)


 Name

    ftok - standard interprocess communication package

 Syntax


    cc  . . .  -lc


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

    key_t ftok(path, id)
    char *path;
    char id;


 Description

    All interprocess communication facilities require you to supply a key
    that the msgget(S), semget(S), and shmget(S) system calls use to obtain
    interprocess communication identifiers.  One suggested method for forming
    a key is to use the ftok subroutine.  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
    conflict.  Therefore, the most significant byte of a key should refer to
    a project.

    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 which
    uniquely identifies a project.  ftok returns the same key for linked
    files when called with the same id and returns different keys when called
    with the same file name but different ids.

 Diagnostics

    ftok returns (keyt) -1 if path does not exist or is not accessible to
    the process.

 Warning

    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 return an
    error.  If the same file is recreated, then ftok is likely to return a
    different key than it did the first time it was called.

 See also

    Intro(S), msgget(S), semget(S), shmget(S)

 Standards conformance

    ftok is not part of any currently supported standard; it is an extension
    of AT&T System V provided by the Santa Cruz Operation.