用C++进行预处理

Question

如何在我同时定义两个指令时,我会得到编译错误？我想要错误

#define ENG
#define POL
#if defined POL
#if defined ENG

这不是

#define ENG
//#define POL
#if defined POL
#if defined ENG

Answer 1

#if defined( ENG ) && defined( POL )
#error You can't define both!
#endif