Bit Fields

[Plasmator]

Hey, I'm just wondering if overflowing is defined and portable when used like so:

	struct myData
	{
		unsigned short s : 2; //limit range to two bits, i.e., 0 to 3 in base 10
	}test = {0};

	++ test.s; //1
	++ test.s; //2
	++ test.s; //3
	++ test.s; //0
	++ test.s; //1
	++ test.s; //2
	//etc...

Is this standard and defined for unsigned types?
What about signed types?

Can my program rely on this behavior and still remain architecture-independent?

Thanks in advance!