On Tue, 2007-04-03 at 21:51 -0400, John Anthony Kazos Jr. wrote:
> > This is wrong. Although the scope is at _block_ level, all variables are
> > allocated on the stack at _function_ level. So, when entering func() all
> > variables within it, including x and y, are allocated.
>
> But this doesn't make sense. Why would the compiler not immediately
> optimize both variables into the same allocation? It seems obvious to me
> that the amount of space pushed onto the stack when the function is
> entered should be the maximum space needed by any combination of local
> variables in-scope at any time. GCC wouldn't be that stupid, would it?
Sorry, the last message was sent before I finished. As I was saying, I
agree, and it depends on the compiler optimization level:
00:21:13 [EMAIL PROTECTED]:~ $> more teste.c
#include <stdio.h>
int main()
{
{
int x=5;
printf("x=%d\n",x);
printf("addr(x)=%p\n", &x);
}
{
int y=10;
printf("y=%d\n",y);
printf("add(y)=%p\n", &y);
}
return 0;
}
00:21:21 [EMAIL PROTECTED]:~ $> gcc -o teste teste.c
00:21:24 [EMAIL PROTECTED]:~ $> ./teste
x=5
addr(x)=0xbffb2200
y=10
add(y)=0xbffb21fc
If you use -O2 or -O3, yes, it works as we expect:
00:22:39 [EMAIL PROTECTED]:~ $> gcc -O2 -o teste teste.c
00:22:46 [EMAIL PROTECTED]:~ $> ./teste
x=5
addr(x)=0xbfd9e7ec
y=10
add(y)=0xbfd9e7ec
Cheers!
-
To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.linux-learn.org/faqs
