Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!ncar!oddjob!nucsrl!morrison
From: morrison@eecs.nwu.edu (Vance Morrison)
Newsgroups: comp.lang.c++
Subject: Re: Proposal for Exceptions for C++
Message-ID: <8180007@eecs.nwu.edu>
Date: 30 Mar 88 16:09:25 GMT
References: <8180006@eecs.nwu.edu>
Organization: Northwestern U, Evanston IL, USA
Lines: 38


	This is in responce to the comments I have seen so far on my
proposal for exception handling for C++.  First may I say that I am glad
to see such a good responce so soon.  Second, I really must apologize for
the incompleteness of my proposal.  I realize that I really did not explain
the semantics of the stack unwinding and other issues well (if at all).
Instead I am relying on the interactive nature of the net to fill in
the gaps as necessary.  Here are some things that need clarification

MEANING OF RAISING AN EXCEPTION
	First let me clarify what happens when an exception is raised.
In my model a search goes on for the most closely nested 'catch' statement
that protects the code in which the exception was raised.t The 'catch' clause
is given control and unless the clase is exited (by using a 'return' 'goto' 
'break' or 'resume' statement), the exception is implictly reraised.
This causes a search for the next layer of 'catch'ing until either a
catch clause is exited or the last chance handler is executed.  

MEANING OF RESUME

	There is some confusion about the meaning of 'resume'  resume
returns control to after the catch clause, NOT TO THE POINT WHERE THE
EXCEPTION OCCURED.   It is IDENTICAL to a goto statement that jumps
right after the 'catch' clause.  That is

	i = j/k; catch {
	    printf("error\n");
	    resume;
			      }
	printf("done\n");

			Is equivalent to 

	i = j/k; catch {
	    printf("error\n");
	    goto out;
				    }
	out:
		printf("done\n");