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.