struct a{
int a;
int b;
};
struct b{
int a;
int b;
}
int main()
{
struct a *p;
struct b b;
p = (struct a *)b; // deste modo da erro
p = (struct a *)&b; ; deste modo o compilador não aponta erro;
}
Would you like to know why?
(struct a *)b is taking a structure and casting cast to a pointer to a structure . That's not possible. A pointer is something very different from a structure.
In this case you are trying to put a structure with two integers inside a pointer. It does not fit. The main point of type struct a * is that it is a pointer. For what it points out is important, but secondary. Primarily it is a pointer.
(struct a *)&b is getting an address for a structure, which is a pointer, and casting cast for a pointer to a structure . It is possible. They are incompatible types, and pointer to pointer.
The & is the operator that takes the address of something, that is, it generates a data that will potentially be a pointer, but will never be a structure.