How to detect negative numbers as parsing errors when reading unsigned integers?

Question

I want to read unsigned integers in base-10 (decimal) representation from a C++ iostream with at least rudimentary error detection. In my view, minus signs would clearly be

Answer 1

Would it be really different if you'd done this?

int i;
unsigned int u;
c >> i;
u = i;
std :: cout << u;

It doesn't matter so much that operator>> tolerates the sign mismatch because the underlying C rules will allow a silent conversion in any case. You're not fundamentally adding any safety by "strengthening" the input operator.

That said, my gcc (4.3.5 on Solaris) says it's a conversion error.