Macro with a C class-CodePudding

I was going through this code (line 41):

https://github.com/black-sat/black/blob/master/src/lib/include/black/logic/parser.hpp

and came across something like this:

#include <iostream>
#define YES

class YES myClass{};

int main(){
cout << "Hi\n";
return 0;
}

What is the purpose of defining a macro and using it in front of a class identifier?

CodePudding user response：

The way you've written it there isn't much point. But if you look at the project's common.hpp file to see how it's used, it makes a lot of sense, and is a common pattern in C and C :

#ifdef _MSC_VER
  #define BLACK_EXPORT __declspec(dllexport)
#else
  #define BLACK_EXPORT
#endif

...

  class BLACK_EXPORT parser
  {
  public:
      ...

Here the author has defined compiler-dependent attributes. If the code is built using MSVC, then any class marked with the BLACK_EXPORT macro will get the dllexport attribute. For other compilers it will do nothing.

CodePudding user response：

If you see, for example:

https://en.cppreference.com/w/cpp/language/class

you'll see that there are a lot of modifiers for a class (for instance, look into the attr optional parameter here: https://en.cppreference.com/w/cpp/language/attributes).

Defining that macro with the required values can adapt the class as required whenever it is included.