Why does the C preprocessor consider enum values as equal?

Question

Why does the std::cout line in the following code run even though A and B are different?

#include 

en         


        

Answer 1

The posts have explained why, but a possible solution for you that keeps readability might be like this

#define MODE_RGB

int main()
{        
    #ifdef MODE_RGB
        std::cout << "RGB mode" << std::endl;
    #elif defined MODE_GREY
        std::cout << "Grey mode" << std::endl;
    #elif defined MODE_CMYK
        std::cout << "CMYK mode" << std::endl;
    #endif
}

You just then need to change the macro at the top, to only the macro you are interested in is defined. You could also include a check to make sure that one and only one is defined and if not then and do #error "You must define MODE_RGB, MODE_GREY or MODE_CMYK