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From: aries@rhi.hi.is (Mimir Reynisson)
Newsgroups: comp.sys.mac.programmer
Subject: Re: C++ method overriding
Message-ID: <2844@krafla.rhi.hi.is>
Date: 27 Feb 91 18:02:43 GMT
References: <2831@krafla.rhi.hi.is> <1991Feb25.214458.11837@ux1.cso.uiuc.edu>
Organization: University of Iceland
Lines: 67

In reference to my previous follow-up:

I discovered MPW C 3.2b3a100 to generate incorrect code for the
following example:

#include <Types.h>
main()
{
	Rect	h;

	Check(h.left);                 // this is ok
	Check((h.left + 1));           // this is ok
	Check((short)h.left + 1);      // this is ok
	Check((short)(h.left + 1));    // we get incorrect code here!
}

What I did was to compile this from the shell and then to call dumpobj
to analyze the code. Here is the dump I made:

00000000: 4E56 FFF8      'NV..'            LINK       A6,#$FFF8
00000004: 302E FFFA      '0...'            MOVE.W     -$0006(A6),D0
00000008: 48C0           'H.'              EXT.L      D0
0000000A: 2F00           '/.'              MOVE.L     D0,-(A7)
0000000C: 4EBA 0000      'N...'            JSR        Check               

00000010: 302E FFFA      '0...'            MOVE.W     -$0006(A6),D0
00000014: 48C0           'H.'              EXT.L      D0
00000016: 5280           'R.'              ADDQ.L     #$1,D0
00000018: 2F00           '/.'              MOVE.L     D0,-(A7)
0000001A: 4EBA 0000      'N...'            JSR        Check               

0000001E: 302E FFFA      '0...'            MOVE.W     -$0006(A6),D0
00000022: 48C0           'H.'              EXT.L      D0
00000024: 5280           'R.'              ADDQ.L     #$1,D0
00000026: 2F00           '/.'              MOVE.L     D0,-(A7)
00000028: 4EBA 0000      'N...'            JSR        Check               

Here is the incorrect part:

0000002C: 302E FFFC      '0...'            MOVE.W     -$0004(A6),D0
                                                        ???? wrong member

00000030: 5240           'R@'              ADDQ.W     #$1,D0
00000032: 48C0           'H.'              EXT.L      D0
00000034: 2F00           '/.'              MOVE.L     D0,-(A7)
00000036: 4EBA 0000      'N...'            JSR        Check             

0000003A: 4E5E           'N^'              UNLK       A6
0000003C: 4E75           'Nu'              RTS        
0000003E: 846D 6169      '.mai'            OR.W       $6169(A5),D2
00000042: 6E00 0000      'n...'            BGT        *+$0002            


I think I could live with this situation if it weren't for the fact that
MPW C++ generates C code that looks like:

	MoveTo((short )(h. left +1), (short )h. top);

Which means that C gets it wrong and I have to do my calculations before
calling my function.s If I havn't said it already then I'll do so now:
this only happens in argument section of a function call not in assignments
(although I haven't tried to do an assignment in the argument section ..
um I wonder if that'd work ..)

Anyway there you have it ...

-MymR