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From: timd@ur-tut.UUCP (Tim D'Ascoli)
Newsgroups: net.micro.mac
Subject: Consulair's Mac C compiler
Message-ID: <605@ur-tut.UUCP>
Date: Mon, 18-Aug-86 11:37:13 EDT
Article-I.D.: ur-tut.605
Posted: Mon Aug 18 11:37:13 1986
Date-Received: Tue, 19-Aug-86 21:02:47 EDT
Distribution: net
Organization: Univ. of Rochester Computing Center
Lines: 46




	I hope that this posting will help someone avoid the "extra" debug time 
that i had to spend when i was using Consulair's Mac C compiler. 
	In The Bible (K & R) on page 94 the following quote can be found, 
"In short, any array and index expression can be written as a pointer and 
offset, and vice versa, even in the same statement.", 
(5:3:6 -- chapter, verse, and paragraph). 

	My problem came with the following code segment:

	/* declared as a global variable */
	char	**inputBuffer;

		/* and then subsequently referenced in another file */
		extern	char	*inputBuffer[];

		/* the following variable was also declared in that file 
		** as a local 
		*/
		char	*inputArray;

		/* and then de-referencing the global in that file */
		inputArray = *inputBuffer;

	Where this inputArray variable pointed to was not where i had intended, 
and when i investigated further i found that when the global variable is 
declared as it was above (extern char *inputBuffer[];) the de-referencing 
generates a LEA.L (load effective address) call. However, when the extern 
declaration is done using the "star star" format 
	(i.e. extern	char	**inputBuffer;),
and the de-reference line left unchanged, the code generated is a MOVEA.L
(move effective address) which gave me what i had expected from the 
de-referencing in the first place.

	Another interesting fact about the Consulair Mac C compiler is that it
generates self modifying code (that may not make a migration to a 
68020 machine).  I found this when i used some of the PBxxxx() calls for 
file i/o. (The location of the trap is AND'ed with a constant to produce the 
desired PB trap call).



		posted in an effort to help.
			- timd