Redefine(#define) reserved c++ key word

Question

Is it possible to redefine a c++ keyword using #define?

#ifdef int
#undef int 
#define int 2
#endif
int main(){
    //Do something with int
}

I

Answer 1

If you're don't use the standard libraries you're allowed to do so. In fact the preprocessor shouldn't distinguish between reserved and non-reserved words.

However that's probably not why you run into problems. First of all your examples don't do what you probably think. The fault is that int is normally not a preprocessor defined macro. The #ifdef int directive will therefore skip the following lines up to the terminating #endif.

What this means is that your second example expands to:

// stuff from iostream and possibly other headers 

int main(){
    cout<

the fault is that cout< simply isn't allowed.