Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!amdahl!pyramid!voder!tolerant!vsi1!steve
From: steve@vsi1.UUCP (Steve Maurer)
Newsgroups: comp.lang.c++
Subject: Re: Proposal for Exceptions for C++
Message-ID: <459@vsi1.UUCP>
Date: 31 Mar 88 19:29:38 GMT
References: <8180006@eecs.nwu.edu> <2229@phoenix.Princeton.EDU> <837@cresswell.quintus.UUCP> <2243@phoenix.Princeton.EDU>
Reply-To: steve@vsi1.UUCP (Steve Maurer)
Organization: Vicom Systems Inc. San Jose, Cal.
Lines: 81

Article 303 of comp.lang.c++:
Path: vsi1!steve
From: steve@vsi1.UUCP (Steve Maurer)
Newsgroups: comp.lang.c++
Subject: Re: Proposal for Exceptions for C++
Message-ID: <457@vsi1.UUCP>
Date: 31 Mar 88 19:26:58 GMT
References: <8180006@eecs.nwu.edu> <2229@phoenix.Princeton.EDU> <837@cresswell.quintus.UUCP> <2243@phoenix.Princeton.EDU>
Reply-To: steve@vsi1.UUCP (Steve Maurer)
Organization: Vicom Systems Inc. San Jose, Cal.
Lines: 71


    I have a question.   What's wrong with doing this?

	Have an exception keyword: "exception", placed before the
	exception processing function.

	Have a identifier following which is the "name" of the
	exception (much like structure identifiers).

	Have a couple of predefined identifiers for the most common
	exceptions: divide by zero, stack overflow, etc.

	use "raise" with these identifiers.

	redefine "resume" to not disturb the flow of control


Example Of Use:

extern int counter;
extern int result;

exception userfoobar		/* a user defined exception */
{
counter--;
}

exception zerodivide		/* zerodivide is a predefined exception	*/
{				/* ...raised on divide by zero errors	*/
counter++;
result = 0;
if (counter > 200) exit();
resume;	/* actually a redundant statement, resume is implicit	*/
}

exception noresume		/* noresume is a predefined exception	*/
{				/* ...raised when resuming generates an	*/
printf("error could not resume\n");		/* immediate error	*/
exit(-1);
}	// exit is also redundant in this case, a few predefined
	// exceptions are automatically fatal (they exit no matter what)

//---------------
int counter, result;

main(int ac; char **av)	/* example use	*/
{
float foo[1000], bar[1000];
int i;
getinputarray(foo);		/* inputs data from somewhere	*/
getinputarray(bar);

for (i = 0; i < 1000; i++)
    {
    result = foo[i] / bar[i];		/* raises exception on / by 0	*/
	/* any other processing	*/	/* increments counter		*/
    }

raise zerodivide;		/* raise a divide by zero exception	*/
raise userfoobar;		/* raise a userfoobar exception		*/
}


    This is simple to use, powerful (though not quite complete), and
would not be too much of a pain to translate into any reasonable C 
implementation (using signals/longjmps).

					Steve Maurer
					tolerant!vsi1!steve
					octopus!vsi1!steve