On Mon, 18 Oct 2010 15:42:31 +0200, Florian Klaempfl wrote about Re: [fpc-pascal] Can variables be declared within a block?:
[snip]
> It's just a matter of readability, e.g. having a variable declared in
> two blocks with the same name can cause you a lot of headache:
>
> procedure p;
>
> begin
> ...
> begin
> var i : integer;
> ...
> ...
> ...
> i:=12341234;
> ...
> ...
> ...
> ...
> end;
> ...
> ...
> ...
> begin
> var i : integer;
> ...
> writeln(i); <--- this i is not the same as above so i does not
> contain 12341234 but it contains probably some garbage.
> end;
This was not usually a problem in ALGOL 60/68, PL/I or C/C++ -- these
languages have supported short scopes for up to 50 years -- as the
programmer was required to be aware of the different scopes of the
like-named variables.
I still use short scoped variables today, usually in C or C++. I have
never had any such problems, even going back almost 40 years when I
programmed in ALGOL 60. All block structured languages require the
programmer to understand the scope of all variables.
Indeed, short scopes can often circumvent name collisions, e.g.
long some_func(unsigned long arg_1)
{
long i; /* procedure/function scoped */
unsigned max_iters;
. . .
/* calculate "i", "max_iters" and any others */
. . .
for (unsigned i = 0; i < max_iters; ++i) /* short scope "i" */
{
/* "i" here is distinct from the one at function scope. */
. . .
}
. . .
return i; /* back to procedure scoped "i". */
}
Whether it is wise to use such lax naming of variables is open to
debate, but at least C and C++ allow the above.
That said, short scoping was never a part of original Pascal. I think
Jensen & Wirth omitted it because it made the compiler simpler.
--
Regards,
Dave [RLU #314465]
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david.w.n...@ntlworld.com (David W Noon)
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