How does memory work in declaration of structure which uses self-referential structure pointer in C/C++?

Question

In declaration of structure in C/C++, we have to use a self-referential structure pointer instead of a structure itself.

// compile error

struct stack {
    int overflow;
    stack p;
}

struct stack {
    int overflow;
    stack* p;
}

One brings about the error but the other doesn't under the same condition(declaration) I'm curious about the operation of memory areas when use stack* p; during the declaration and how to make it possible.

Answer 1

This

struct stack {
    int overflow;
    stack p;
}

Tries to contains itself , so how big should it be? With one copy of itself it would look line this

 int ov;
 {
     int ov;
     stack p;
 }

but that stack p needs to be expanded - so we get

 int ov;
 {
     int ov;
    {
         int ov;
         stack p;
    }
 }

but that stack p needs to be expanded - so we get

 int ov;
 {
     int ov;
    {
         int ov;
         {
             int ov;
             stack p;
          }
    }
 }

but that stack p needs to be expanded - so we get ...... forever.

Look at another way, how many int overflows should the struct contain?

The pointer one works like this

  int overflow;
  stack *p;

The end. The struct is of a well defined size an integer and a pointer