Re: typedefs and structs

[Vadim Lobanov <vlobanov@speakeasy.net>]

On Wed, 9 Nov 2005, linux-os \(Dick Johnson\) wrote:

>
> On Wed, 9 Nov 2005, linas wrote:
>
> > On Wed, Nov 09, 2005 at 08:22:15AM -0800, Vadim Lobanov was heard to remark:
> >> On Wed, 9 Nov 2005, J.A. Magallon wrote:
> >>
> >>> void do_some_stuff(T& arg1,T&  arg2)
> >>
> >> A diligent C programmer would write this as follows:
> >> 	void do_some_stuff (struct T * a, struct T * b);
> >> So I don't see C++ winning at all here.
> >
> > I guess the real point that I'd wanted to make, and seems
> > to have gotten lost, was that by avoiding using pointers,
> > you end up designing code in a very different way, and you
> > can find out that often/usually, you don't need structs
> > filled with a zoo of pointers.
> >
>
> But you can't avoid pointers unless you make your entire
> program have global scope. That may be great for performance,
> but a killer if for have any bugs.

Just to extract some useful technical knowledge from the current ongoing
"flamewar"...
I'm not entirely sure if the above statement regarding performance is
correct. Some enlightenment would be appreciated.

Suppose you have the following code:
	int myvar;
	void foo (void) {
		printf("%d\n", myvar);
		bar();
		printf("%d\n", myvar);
	}
If bar is declared in _another_ file as
	void bar (void);
then I believe the compiler has to reread the global 'myvar' from memory
for the second printf().

However, if the code is as follows:
	void foo (void) {
		int myvar = 0;
		printf("%d\n", myvar);
		bar(&myvar);
		printf("%d\n", myvar);
	}
If bar is declared in _another_ file as
	void bar (const int * var);
then I think the compiler can validly cache the value of 'myvar' for the
second printf without re-reading it. Correct/incorrect?

-Vadim Lobanov
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/