Re: asm/unistd.h

["J . A . Magallon" <jamagallon@able.es>]

On 04.05 Andreas Schwab wrote:
> 
> Try this and watch your compiler complaining:
> 
> #define foo() { }
> #define bar() do { } while (0)
> void mumble ()
> {
>         if (1) foo(); else bar();
>         if (2) bar(); else foo();
> }
> 

Perhaps it is time to USE gcc, yet the kernel can be built only with gcc.
IE, use statement expressions.

Try this:

#define foo() ({ })
#define bar() do { } while (0)
void mumble ()
{
	if (1) foo(); else bar();
	if (2) bar(); else foo();
}

and see you compiler shutup.
You can even declare vars inside the ({ ... }) block,
so all the

#define bar(x) do { use_1(x); use_2(x); } while (0)

could be written like:

#define bar(x) ({ use_1(x); use_2(x); })

Even you can use <typeof>:

#define swap(a,b) \
({ typeof(a) tmp = a; \
   a = b; \
   b = tmp; \
})

int main()
{
	int a,b;
	double c,d;
	
	swap(a,b);
	swap(c,d);
}

Its correct in egcs-1.1.2 and up, so it is safe for use in kernel 2.4.
Do not know if previuous gcc eats it up.

-- 
J.A. Magallon                                          #  Let the source
mailto:jamagallon@able.es                              #  be with you, Luke... 

Linux werewolf 2.4.3-ac3 #1 SMP Thu Apr 5 00:28:45 CEST 2001 i686