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c++unsigned

casting signed to unsigned

is it correct to do this?

typedef unsigned int Index;

enum
{
  InvalidIndex = (Index) -1 
};

I have read that it is unsafe across platforms, but I have seen this in so many "professional" codes...

Solution

  • What you read was probably out of Fear, Uncertainty and Doubt. The author of whatever you read probably thought that (unsigned)-1 was underflowing and potentially causing chaos on systems where the bit representation doesn't happen to give you UINT_MAX for your trouble.

    However, the author is wrong, because the standard guarantees that unsigned values wrap-around when they reach the edge of their range. No matter what bit representations are involved, (unsigned)-1 is std::numeric_limits<unsigned>::max(). Period.

    I'm not sure what the benefit of it is here, though. You're going to get that large, maximum value.. If that is fine, I guess you're good to go.