> Dear All,
>
> 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.
I do not think this issue is kernel related as much as it may be your
inexperience with C. the macro expands to
1 = 2
you are not assigning a varible, you are trying to assign a constant.
When the GCC sees this its context checking catches it and gives you the
eror. Perhaps you overlooked this accidentally? or maybe you just dont
know the C preprocessor very well. In any case, it is pretty simple to
rectify, look for "The C Programming Language" by Kernighan and Ritchie
Kris
P.S. Is this off topic for this list?
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