Technical Q&A's

OPS 10 - Impossibility of Extracting File System Information from the WindowPtr (14-May-96)

Q I need to get the full pathname to a document in a callback where the only relevant piece of information I have is the WindowPtr for the window that will contain the document. I know the filename, but I do not know the directory ID or volume reference number. Is there any way to obtain the dirID and vRefNum from the WindowRecord?

A Unfortunately, there is no way to extract the file system information you need from a WindowRecord. The WindowRecord includes only structural human interface information which might include the file name (actually the document's title). Windows provide a means of presenting the data of documents for the user, but the WindowRecords have no knowledge of where to find the file system information. As you have implied, you must have the directory ID and volume reference number to extract a full pathname.

Knowing the vRefNum and the parent dirID, you would be able to use one of the FullPath routines in the DTS Sample Code MoreFiles.

If you knew the file reference number, you could call PBGetFCBInfo() to get the vRefNum and dirID, then use MoreFiles to get your full pathname. PBGetFCBInfo() gives information about open files (files in the file control block queue). You call PBGetFCBInfo() like this:

 pascal	OSErr	GetFileLocation(short refNum,
		short *vRefNum,
		long *dirID,
		StringPtr fileName)
 {
 	FCBPBRec pb;
 	OSErr error;
 
 	pb.ioNamePtr = fileName;
 	pb.ioVRefNum = 0;
 	pb.ioRefNum = refNum;
 	pb.ioFCBIndx = 0;
 	error = PBGetFCBInfoSync(&pb);
 	*vRefNum = pb.ioFCBVRefNum;
 	*dirID = pb.ioFCBParID;
 	return (error);
 }

See Also:

For more information on File Control Blocks, see Inside Macintosh: Files, pp. 2-81 through 2-83.
For more information on PBGetFCBInfo, see Inside Macintosh: Files, pp. 2-237 through 2-238.

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