Why is NULL undeclared?

Question

I have a problem with this struct contructor when I try to compile this code:

typedef struct Node
{
    Node( int data ) //
    {
        this->data = dat         


        

Answer 1

Do use NULL. It is just #defined as 0 anyway and it is very useful to semantically distinguish it from the integer 0.

There are problems with using 0 (and hence NULL). For example:

void f(int);
void f(void*);

f(0); // Ambiguous. Calls f(int).

The next version of C++ (C++0x) includes nullptr to fix this.

f(nullptr); // Calls f(void*).