The type of the C struct field is not fully

struct strct{
int i;
struct STRCT struct1;//compiled pass, said to be variable Struct1 type not exactly
};
But
struct strct{
int i;
struct STRCT *struct1;//can be completely
};

In fact, more thinking on the coming out, the first structure of the Reference object, object re-reference object, so always nested down, the compiler certainly do not know you this

How many bytes of struct type are placed;

The second one is different, because he is the pointer, storing a struct strct points to the memory address, is a fixed size, 4Bytes.