Macro doesn't handle bool conditions when they are "inline" but works via variable

Question

I've written a basic macro which asserts regardless of debug or not:

#define ASSERT_ALWAYS(cond) \
    do                      \
    {                       \
        if (!cond)          \
        {                   \
            std::abort();   \
        }                   \
    } while(0)              \

The strange thing is it compiles if I use a variable:

const bool s = myObj.anEnum != AnEnum::C;
ASSERT_ALWAYS(s);

but without the variable this doesn't compile:

ASSERT_ALWAYS(myObj.anEnum != AnEnum::C);

I get this compiler error:

error: no match for ‘operator!’ (operand type is ‘AnEnum::C’)
no known conversion for argument 1 from ‘AnEnum::C’ to ‘bool’

AnEnum is declared like this:

enum class AnEnum : char {
  A = '0',
  B = '2',
  C
};

I get similar compiler errors for other types I try to change, so is the problem with my macro?

Answer 1

When you use the expression, the preprocessor pastes

if(!myObj.anEnum != AnEnum::C)

so the compiler processes

if( (!myObj.anEnum) != (AnEnum::C) )

and the error makes more sense.

What you need is if(!(cond)).