Is it safe to #define NULL nullptr?

Question

I have seen below macro in many topmost header files:

#define NULL 0  // C++03

In all over the code, NULL and 0 are u

Answer 1

While it might break backwards-compatibility with older stuff that was badly written (either that, or overly clever...), for your newer code, this is a non-issue. You should use nullptr, and not NULL, where you mean nullptr. Also, you should use 0 where you mean zero.