Definitely look at Objective-C.
typedef struct objc_object {
Class isa;
} *id;
typedef struct objc_class {
struct objc_class *isa;
struct objc_class *super_class
const char *name;
long version;
long info
long instance_size;
struct objc_ivar_list *ivars;
struct objc_method_list **methodLists;
struct objc_cache *cache;
struct objc_protocol_list *protocols;
} *Class;
As you can see, inheritance information, along with other details is held in a class struct (conveniently the class can also be treated as an object).
Objective-C suffers in the same manner as C++ with encapsulation in that you need to declare your variables publicly. Straight C is much more flexible in that you can just return void pointers that only your module has internal access to, so in that respect encapsulation is much better.
I once wrote a basic OO style C paint program as part of a graphics course - I didn't go as far as the class declaration, I simply used a vtable pointer as the first element of the struct and implemented hand-coded inheritance. The neat thing about playing around with vtables at such a low level is that you can change class behaviour at runtime by changing a few pointers, or change on objects class dynamically. It was quite easy to create all sorts of hybrid objects, fake multiple inheritance, etc.
