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From: vince@cvs.rochester.edu (Vincent Ferrera)
Newsgroups: comp.sys.mac.system,comp.sys.mac.programmer
Subject: OS queues and the File Manager
Message-ID: <12959@ur-cc.UUCP>
Date: 25 Mar 91 16:38:23 GMT
Sender: news@uhura.cc.rochester.edu
Organization: Center for Visual Science, U. of Rochester
Lines: 32


	I am trying to write an application in C which will access 
	information in the volume-control-block queue.  Looking in 
	Inside Mac v. II, I noticed that all the queue elements for all
	OS queues are defined as a variant record in Pascal.  I tried the
	following code:
		
		QHdrPtr vcb_head;
		QElemPtr vcb_elem;
		
		vcb_head = GetVCBQHdr();
		vcb_elem = (*vcb_head).qHead;
		
	I naively assumed that I could then access the information in the 
	volume control block by simply doing, e.g.
	
		volname = (*vcb_elem).vcbVN;
		
	To which the Think C compiler responded, "Surely you jest, I don't
	know anything about struct/union member 'vcbVN'."  Using the
	debugger, I found that (*vcb_elem) contained only three fields:
	qLink, qType, and qData.  Furthermore, qData was just an array, not
	a struct.  I looked at the elements of qData and could figure out
	roughly which ones corresponded to the vcb info I wanted, but this
	struck me as an inelegant solution.  Does anyone know a better way?
	Is there a general method for translating pascal variant record
	into C?
	
	Just asking,
	
	Vincent Ferrera