Hello Michael,
Michael Sperber wrote:
> I have a few questions regarding goto:
>
> The standard says:
>
> "It is not allowed to jump into a sequence of statements defined in a
> compound statement (i.e. alt statement, while loop, for loop, if-else
> statement, do- while loop and the interleave statement)."
>
> Is it allowed to jump between the alternatives of an alt statement?
>
I think that would be a special case of the mentioned jump into an alt
statement.
So, no, I don't think so (and I don't think it makes much sense, either).
As far as I can remember, the goto was introduced into the language
after labeled break and continue statements (as in Java) were proposed
to be added to the standard, to allow breaking/continuing of nested
loops in a more straightforward way.
Its intention was never to allow to break the proper flow semantics of
structured programming.
> Consider the situation where a forward goto goes over a declaration,
> i.e. like this:
>
> control {
> goto forward;
>
> var integer i := 5;
>
> forward:
>
> ... i ...
> }
>
>
As far as I know, all variable declarations have to come at the
beginning of a block before any control statements (like goto).
Thus, you would need to modify your example to something like to be
allowed TTCN-3:
goto forward;
...
{
var integer i := 5;
...
label forward;
... i ...
}
However, since the variable declaration with initialization is simply
syntactic sugar for a declaration (which is not a statement in itself,
but only meta information about this scope for the compiler to be able
to check type-correctness) without initialization and an additional
assignment, I think the result of jumping over the assignment would be
that the variable still is declared, but (if it is not assigned after
the jump label) not initialized, leading to a runtime error, if it is
used as Rvalue.
> Does the standard say anything about i in this case, i.e. if the use of
> i is a violation, or if it's OK to use it, but its value is unspecified,
> or undefined?
>
I'm sure it does, somewhere.
> Help would be much appreciated!
>
>
Best regards,
Jacob Wieland
--
Jacob Wieland
Software Engineer
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