Re: How to exit out of a function ? what is try-catch-throw in terms of Program Counter

["Alf P. Steinbach" <alfps@start.no>]

* Alf P. Steinbach:
> * David Thompson:
>> On Sun, 21 Oct 2007 00:55:53 +0200, "Alf P. Steinbach"
>> <alfps@start.no> wrote:
>>
>>> * gnuist006@gmail.com:
>>
>>>> NOTE: I am really afraid of try-catch-throw. I have never been
>>>> able to understand it since it does not exist in C and I cant
>>>> really visualize the construct in terms of C. <snip>
>>> The closest equivalent in C would be a 'longjmp'.  However, a C++ 
>>> exception is more limited, in that it will only jump up the call chain, 
>>
>> C longjmp/setjmp also is only guaranteed to work up the stack; the
>> fact that _some_ implementations can work cross-stack and in
>> particular cross-thread is not standard nor portable.
> 
> So?
> 
> But also, what on Earth do you mean by a cross-thread longjmp?  I 
> implemented coroutines in terms of longjmp at the time that was popular, 
> so the concepts involved are not unfamiliar to me.  Yet I fail to 
> envision what you could be talking about, especially as "fact".  I think 
> perhaps you're talking about restoring the full context (registers etc) 
> of a moment in a thread's execution?
> 
> 
>>> and it's more powerful, in that it will destroy local objects as it 
>>> does so.  Also, if you use 'longjmp' in C++ you're practically doomed 
>>> (unless you use it to jump between co-routines with their own 
>>> stacks), because 'longjmp' doesn't destroy local objects.
>>>
>> Actually it's Undefined Behavior; a good quality C++ implementation
>> CAN coordinate longjmp, and also pthreads cancellation, with
>> exceptions to destruct locals cleanly -- but it's not required.
> 
> I don't know about ptheads cancellation, but other than that you're 
> right.  Visual C++ coordinates longjmp with C++ stack unwinding.  g++, 
> on the other hand, does not.

Sorry, I didn't see the weasel-word "actually", which indicates a 
contradiction.

When I wrote that you're right, that just meant that you supplied some 
extra info that wasn't incorrect.

Cheers,

- Alf


-- 
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?