Legacy Document

Inside Macintosh: Interapplication Communication /

Chapter 2 - Edition Manager / Subscribing to Non-Edition Files

Calling a Format I/O Function

To indicate to the Edition Manager which format I/O function to use, use the CallFormatIOProc function.

err := CallFormatIOProc (selector, PB, routine);

Set the selector parameter to one of the format I/O verbs. The format I/O verbs include

• ioHasFormat
• ioReadFormat
• ioNewFormat
• ioWriteFormat

The PB parameter of the CallFormatIOProc function contains a format I/O parameter block.

TYPE FormatIOParamBlock = 
   RECORD
      ioRefNum:      LongInt;       {reference number}
      format:        FormatType;    {edition format type}
      formatIndex:   LongInt;       {opener-specific enumeration }
                                    { of formats}
      offset:        LongInt;       {offset into format}
      buffPtr:       Ptr;           {data starts here}
      buffLen:       LongInt;       {length of data}
   END;

The routine parameter of the CallFormatIOProc function is a pointer to a format
I/O function.

The following list shows which fields of FormatIOParamBlock are used by the format I/O verbs:

Format I/O verb		Parameter	Description	Called by
ioHasFormat	-->	ioRefNum	I/O reference number returned by opener.	EditionHasFormat, GetStandardFormats, and ReadEdition functions
	-->	format	Check for this format.
	<--	formatIndex	An optional enumeration of the supplied format.
	<--	buffLen	If found, return the length size or -1 if size is unknown.
	<--	Return value	A noErr or noTypeErr code.
ioReadFormat	-->	ioRefNum	I/O reference number returned by opener.	ReadEdition and GetStandardFormats functions
	-->	format	Get this format.
	-->	formatIndex	Value returned by ioHasFormat.
	-->	offset	Read format beginning from this offset.
	-->	buffPtr	Put data beginning here.
	<->	buffLen	Specify buffer length to read, and return actual amount received.
	<--	Return value	A noErr code, or appropriate error code.
ioNewFormat	-->	ioRefNum	I/O reference number returned by opener.	SetEditionFormatMarkand WriteEdition functions
	-->	format	Create this format.
	<--	formatIndex	An optional enumeration of the supplied format.
	<--	Return value	A noErr code, or appropriate error code.
ioWriteFormat	-->	ioRefNum	I/O reference number returned by opener.	WriteEdition function
	-->	format	Get this format.
	-->	formatIndex	Value returned by ioNewFormat.
	-->	offset	Write format beginning from this offset.
	-->	buffPtr	Get data beginning here.
	<->	buffLen	Specify buffer length to write.
	<--	Return value	A noErr code or appropriate error code.

The marks for each format are kept by the Edition Manager. The format I/O function only needs to be able to read or write, beginning at any offset. If you know that your application always reads an entire format sequentially, you can ignore the offset.