how to use #if,#else,#endif... inside c macro

Question

 #include < iostream >  

 #define MY_CHK_DEF(flag) \
 #ifdef (flag) \
    std::cout<<#flag<<std::endl; \
 #else \
    std::cout<<#flag<<" ,flag not define"<<std::endl; \
 #endif 


 int main()
 {
    MY_CHK_DEF(FLAG_1);
    MY_CHK_DEF(FLAG_2);
    MY_CHK_DEF(FLAG_3);
    ...  
 }

complier report:

main.cpp:3:24: error: '#' is not followed by a macro parameter

any ideas?

Thanks

Answer 1

You actually can do this if you use BOOST processor header lib.. it provides a BOOST_PP_IF macro allow this type of decisions.

http://www.boost.org/doc/libs/1_53_0/libs/preprocessor/doc/ref/if.html