On Fri, 2006-02-17 at 19:01 +0530, Mukund JB. wrote:
[...]
> I have seen a macro like this in the Linux kernel sources in
> include/linux/usb.h line no: 1090.
>
> #define usb_dotoggle(dev, ep, out) ((dev)->toggle[out] ^= (1 << (ep)))
>
> I did not understand how it works?
> I have written a small usermode program to test this.
>
> #define x 1
> #define y 2
> #define macro() (x = y)
> main()
> {
> int abc = macro();
> printf("abc = %d\n",abc);
> }
>
> This code results in a compile error.
> test.c:9: error: invalid lvalue in assignment.
>
> Why?
Find the option to tell gcc to stop after preprocessing, use it, look at
the resulting file (you can specify it with -o) and you will see it
pretty clearly.
Bernd
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