C Primer Plus®, Third Edition

Pointer Type-Checking

C++ is stricter about pointer assignments than C is. You can't assign a pointer of one type or a numeric value to a pointer of a second type unless you use an explicit type cast.

int x;
int * pi;
short *ps;
pi = &x;               /* ok, both type int       */
pi = 0xB8000;          /* ok in C, invalid in C++ */
pi =  (int *) 0xB8000; /* ok in C, C++            */
ps = pi;               /* ok in C, invalid in C++ */
ps = (short *) pi;     /* ok in C, C++            */

There are a couple of exceptions. In C++, as in C, you can assign a pointer of any type to a pointer-to-void, but, unlike C, you cannot assign a pointer-to-void to another type unless you use an explicit type cast.

 int ar[5] = {4, 5, 6,7, 8}; int * pi; void * pv; pv = ar; /* ok in C, C++ */ pi = pv; /* ok in C, invalid in C++ ...