On Tuesday, 16 July 2013 at 01:13:15 UTC, H. S. Teoh wrote:
On Mon, Jul 15, 2013 at 08:59:44PM -0400, Jonathan M Davis
wrote:
On Monday, July 15, 2013 14:48:08 Manfred Nowak wrote:
> Jonathan M Davis wrote:
> > gotos in such a context seem like a bit
> > of a nightmare to me though.
>
> I did realize this nightmare. Therefore the assurance in the
> docs
> is probably true only in the absence within the scope of at
> least
> gotos to targets within the scope.
Well, I'd have to study exactly how goto works to say how
exactly it
would interact with stuff like try-catch. I've pretty much
only used
goto with case statements and loops and haven't spent the time
trying
to sort out all of its idiosyncracies. I guess that I should
add that
to be my todo list.
[...]
My understanding is that goto translates directly to a jump in
assembly,
so jumping in/out of blocks with declarations or stuff that
needs
cleanups should immediately raise red flags. Of course, the
compiler may
do something intelligent by inserting implicit stack pointer
adjustments
and/or cleanup blocks, but I wouldn't count on it unless the
language
spec explicitly requires so.
T
That's wrong. That's "longjmp", which does a raw ASM jump.
C's goto correctly handles stack decrement if the jump would make
you leave a scope (destroying a variable), and make a variable
disappear. goto's aren't allowed to jump over declarations
(unless they "skip" a scope entirelly). Some implementations
allow it, but I have no idea how they non-POD type construction
:S but stack pointer is always correctly handled.
With C++'s destructors, goto has also been "improved" to
guarantee that the destructor is called when a goto would make a
variable leave a scope. In C++, I don't think it is possible to
"leak" a stack variable's destructor, short of doing a longjmp.
Long story short, in C, goto always perfectly safe (AFAIK). In
C++, it depends on what the compiler will allow you to to do,
depending on its "features". If it respects "strict ANSI",
though, then you shouldn't be able to go wrong.
--------
Related: I use goto fairly often, but I've yet to find a use-case
for it outside of loop "improvement", or goto end cleanup. In
both these cases, scope blocks should not be a problem.
