MACRO - How is it working in Linux

["Mukund JB." <mukundjb@xxxxxxxxxxxxxxxxxxxxx>]

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.

Why?
 
Regards,
Mukund Jampala


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