Silly #define Question

[Plasmator]

Hey, I feel silly for asking this, but, say if I do:

#define abcdefg 12345

void Test(){cout<<abcdefg;}

This will work on all standards conforming C++ compilers, right?

I mean, is it safe to use #define to define something? Will this glorified search & replace work on all preprocessors?

Thanks in advance,
sorry for such a retarded question.

Edit: Ah, I just remembered about NULL, is this a standard #define, or something that's Microsoft (and others) specific?