Why so many parentheses in SUCCEEDED macro?

Question

Windows SDK features SUCCEEDED macro:

#define SUCCEEDED(hr) (((HRESULT)(hr)) >= 0)
-----------------------^-------------^-----

clearly as with other macros there're parentheses to ensure right interpretation of the intent by compiler.

What I don't get is why there are parentheses around (HRESULT)(hr) (I marked them with ^ character). hr is parenthesized so that some complex construct can be there, HRESULT is parenthesized to form a C-style cast, then the whole >= construct is parenthesized as well, so why the extra pair of parentheses around (HRESULT)(hr)?

Answer 1

The C standard puts the cast at a higher precedence than the comparison, so the parens are not required for the complier.

However, people read the macro definition, and putting them in makes the precedence explicit, so that it is obvious to people reading it that it is the result of comparing ((HRESULT)hr) with zero rather than casting the result of the comparison without having to think about the precedence.

Answer 2

The extra parentheses don't change the meaning, but they do make the precedence explicit. Without them, a reader who didn't know all the precedence rules would have to work out what the expression meant.

To clarify, I'm only referring to the parentheses around the cast expression, as marked in the question. The others are necessary (unless the macro were only intended for C++ and not C, in which case you could change the (HRESULT)(hr) to HRESULT(hr)).