As shown above, the iffhandle structure contains the public field
iff_Stream.  This is a longword that must be initialized to contain
something meaningful to the stream manager.  IFFParse never looks at this
field itself (at least not directly).  Your iff_Stream may be an AmigaDOS
filehandle, or an IFFParse ClipboardHandle, or a custom stream of any type
if you provide your own custom stream handler (see the section on
"custom stream handlers" later in this chapter).  you must initialize your
IFFHandle structure's iff_Stream to your stream, and then initialize the
IFFHandle's flags and stream hook.

Three sample initializations are shown here.  In the case of the internal
DOS stream manager, iff_Stream is an AmigaDOS filehandle as returned by
open():

    iff->iff_Stream = (ULONG) Open ("filename", MODE_OLDFILE);
    if(iff->iff_Stream) InitIFFasDOS (iff);
        /* use internal DOS stream manager */

In the case of the internal Clipboard stream manager, iff_Stream is a
pointer to an IFFParse ClipboardHandle structure (the openclipboard() call
used here is a function of iffparse.library, not the clipboard.device):

    iff->iff_Stream = (ULONG) OpenClipboard (PRIMARY_CLIP);
    InitIFFasClip (iff); /* use internal Clipboard stream manager  */

When using a custom handle such as an fopen() file handle, or a device
other than the clipboard, you must provide your own flags and stream
handler:

    iff->iff_Stream = (ULONG) OpenMyCustomStream("foo");
    InitIFF (iff, IFFF_FSEEK | IFFF_RSEEK, &mystreamhook);

IFFParse "knows" the seek capabilities of DOS and ClipboardHandle streams,
so initiffasdos() and initiffasclip() set the flags for you.

    You May Change the Seek Bits in iff_Flags:
    ------------------------------------------
    IFFParse sets IFFF_FSEEK | IFFF_RSEEK for DOS files.  This is not
    always true (e.g., pipes).  If you know that a DOS file has different
    seek characteristics, your application may correct the seek bits in
    iff_Flags after calling initiffasdos().

When using initiff() to provide a custom handler, you must also provide
flags to tell IFFParse the capabilities of your stream.  The flags are:


    IFFF_FSEEK:  This stream has forward-seek capability only.
    IFFF_RSEEK:  This stream has random-seek capability.
                 IFFF_RSEEK tends to imply IFFF_FSEEK, but it's
                 best to specify both.


If neither flag is specified, you're telling IFFParse that it can't seek
through the stream.

After your stream is initialized, call openiff():

    error = OpenIFF (iff, IFFF_READ);

Once you establish a read/write mode (by passing IFFF_READ or IFFF_WRITE),
you remain in that mode until you call closeiff().