Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!agate!garnet.berkeley.edu!elcond
From: elcond@garnet.berkeley.edu (Gregory Dow)
Newsgroups: comp.sys.mac.programmer
Subject: Bug in LSC
Message-ID: <7216@agate.BERKELEY.EDU>
Date: 27 Feb 88 00:03:55 GMT
Sender: usenet@agate.BERKELEY.EDU
Reply-To: elcond@garnet.berkeley.edu.UUCP (Gregory Dow)
Organization: University of California, Berkeley
Lines: 45
Keywords: C, Bug

I have tripped over what appears to be a bug in LightSpeed C's CallPascal
routines.  When calling a Pascal function (a function declared as pascal
so that it may be used as a toolbox hook) indirectly through a pointer,
the LSC manual (page 9-7) states that you must use the one of the
CallPascal library functions.  The argument list to CallPascal should be
the arguments to your function, with a pointer to your function as a
last, extra argument.

This is necessary because the calling conventions in C and Pascal are
different:  they put the arguments on the stack in different orders.
However, when I tried calling CallPascal with my function pointer as the
last argument, the system crashed because it tried to treat my FIRST
argument as a function pointer.  Reversing the order of the arguments
to CallPascal worked.  It appears that CallPascal is confused about in
which to pass the arguments.

Example:

pascal void MyFunc(arg1, arg2)
{
... some code
}


	Calling MyFunc from another function:

typedef  void (*VoidFunc());
VoidFunc  funcPtr;

CallPascal(arg1, arg2, funcPtr);
	/* does not work.  Thinks arg1 is a function pointer */


CallPascal(funcPtr, arg2, arg1);
	/* This works.  Order of arguments is reversed */

(*funcPtr)(arg2, arg1);
	/* This also works because C passes argmument from left-to-right */
	/* and Pascal from right-to-left.				 */



  Gregory Dow			ARPA:   elcond@garnet.berkeley.edu
  Chemical Engineering Dept.	UUCP:   {uwvax, decvax, ihnp4, ...}!ucbvax
  University of California	          !elcond%garnet.berkeley.edu
  Berkeley, CA  94720		BITNET: POLYDOW@UCBCMSA