Null pointer in C++

Question

When in C++ I declare a null pointer to be int* p=0, does that mean the zero is some special constant of integer pointer type, or does it mean that p

Answer 1

Yes. Zero is a special constant. In fact, it's the only integral constant which can be used, without using explicit cast, in such statements:

int *pi = 0;  //ok
char *pc = 0; //ok
void *pv = 0; //ok
A *pa = 0;    //ok

All would compile fine.

However, if you use this instead:

int *pi = 1;  //error
char *pc = 2; //error
void *pv = 3; //error
A *pa = 4;    //error

All would give compilation error.

In C++11, you should use nullptr, instead of 0, when you mean null pointer.