Re: [boost] Re: improved assertions?

From: Victor A. Wagner, Jr. (vawjr_at_[hidden])
Date: 2002-06-20 14:44:52

possibly off-topic----------- apologies, if so.

Mayhaps the problem here is caused by an unfortunate interpretation by the 
Standards Committee to the "Resumption vs. Termination" (Stroustrup "The 
Design and Evolution of C++" section 16.6) arguments during the 
standardization process.  As an example, Stroustrup ("The C++ Programming 
Language Third Edition" section 14.4, last paragraph) says: ''The process 
of searching "up through the stack" to find a handler for an exception is 
commonly called "stack unwinding."  As the call stack is unwound, the 
destructors for constructed local objects are invoked.''

Bjarne (and apparently the committee (I wasn't there, can't comment 
further)) erred in the assumption that "searching up the stack" and 
"unwinding (implying destructors being called)" are the same thing, they 
are not.  Perhaps in their zeal to make C++ exceptions "Termination" rather 
than "Resumtion" model they decided that the stack _should_ be "unwound" 
before the exception handler is invoked.  Of course "unwinding" the stack 
makes "resumption" _impossible_ not simply " resumption violates the standard".

In my opinion, this decision hinders effective debugging so badly that it 
should be re-considered (If I knew how to write such a suggestion, I would 
certainly so do).  I have NO argument with the "termination" semantics, I 
object to the "destructors being called up the line" until the appropriate 
"catch" is found.

Think how _simple_ it would be to provide a "stack trace" if the stack were 
still intact!!
Think of how much information would be available to a modern debugger!!
The implementation can't be _that_ difficult, Microsoft's Structured 
Exception Handling does it (it has both resume and termination semantics).
The implementation shouldn't be all that much slower either.  One simply 
puts a new "frame" on the stack for the exception "handler" and "unwinds 
the stack" when it returns.

At Thursday 2002/06/20 05:27, you wrote:
>[deleted]
>
>The immediate need I had was, a low-level function contains an
>assert.  I gave the code to an associate, who quickly triggered the
>assertion.  I couldn't easily tell where it came from since it could
>have been called on various paths.  I would have liked to see a
>traceback showing the path through my code, maybe up to main.
>
>I personally don't often use exceptions.  By default on my environment
>(linux/g++) they provide no information to the user that can be fed
>back to the programmer (other than a core).  In most cases the core is
>useless when compiled with high optimization on g++.
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Victor A. Wagner Jr.      http://rudbek.com
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