The only change that might affect people is the type of
     NULL: while it is required to be a macro,
     the definition of that macro is not allowed
     to be (void*)0, which is often used in C.
    
     For g++, NULL is
     
#define
'd to be
     __null, a magic keyword extension of
     g++.
    
     The biggest problem of #defining NULL to be
     something like “0L” is that the compiler will view
     that as a long integer before it views it as a pointer, so
     overloading won't do what you expect. (This is why
     g++ has a magic extension, so that
     NULL is always a pointer.)
    
In his book Effective
    C++, Scott Meyers points out that the best way
    to solve this problem is to not overload on pointer-vs-integer
    types to begin with.  He also offers a way to make your own magic
    NULL that will match pointers before it
    matches integers.