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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)?
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The macro and its parameters should be enclosed in parentheses. When macro parameters or expression are not parenthesized, the intended logic may get disrupted after expanding the macro.
The invocation of the macro need not be restricted to a single logical line—it can cross as many lines in the source file as you wish. The number of arguments you give must match the number of parameters in the macro definition.
#define is a useful C++ component that allows the programmer to give a name to a constant value before the program is compiled. Defined constants in arduino don't take up any program memory space on the chip. The compiler will replace references to these constants with the defined value at compile time.
The #define directive is used to define values or macros that are used by the preprocessor to manipulate the program source code before it is compiled. Because preprocessor definitions are substituted before the compiler acts on the source code, any errors that are introduced by #define are difficult to trace.
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.
175
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)).
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