C ++ #define值未在cpp文件中读取

Question

In my C++ .h file:

class foo {
#define useThis true

...
}

In my .cpp file:

#if useThis
... generate A code
#else
... generate B code
#endif

The problem is that the #define values are not being read in the .cpp file, so what is happening is both A and B are being generated.

I am including the .h file in the top of the .cpp file.

Answer 1

Boolean value can not be used in macros for some compilers, like Visual Studio (works under g++ though). A cross compiler way should be:

#define useThis 1

Or, define a macro without value, and use ifdef to test if it has been defined:

#define useThis

#ifdef useThis
    ...
#else
    ...
#endif