Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!usc!apple!marc
From: marc@Apple.COM (Mark Dawson)
Newsgroups: comp.sys.mac.programmer
Subject: passing correct var size in MPW C/C++
Message-ID: <43315@apple.Apple.COM>
Date: 24 Jul 90 22:48:46 GMT
References: <26ACA0CB.542F@wilbur.coyote.trw.com>
Distribution: usa
Organization: Apple Computer Inc, Cupertino, CA
Lines: 37

I wrote a routine in assembly that I wanted to call from my C++ code, it
didn't end up working the way I expected--the C++ call kept passing a long,
when my assembly was expecting a short (2 bytes).  I've of course modifed
my assembly to expect a long, but I'd like to know where my thinking went
wrong.

extern "C" void myProc(short x);  // external declaration

....
short vRefNum = -2;
myProc(vRefNum);  // I also tried myProc((short)vRefNum) and got the same res
...
--------
myProc	PROC  EXPORT
        ....
        move.l	(sp)+,A0	// pop return @ off stack
        move.w	(sp)+,D0	// get vRefNum off stack
       ....
        ENDP

--------
When I did a debugger trap in myProc(), the stack always had an $FFFF FFFE,
not the $FFFE that I expected--it seemed to be passing 4 bytes instead of two.
Why?

Thanks,

Mark


-- 
---------------------------------
Mark Dawson                Service Diagnostic Engineering
AppleLink: Dawson.M

Apple says what it says; I say what I say.  We're different
---------------------------------