Is it possible to do inheritance from an abstract/base struct or simulate something along those lines in C?

Question

I am currently working with a C program that uses structs composed of xyz coordinates, but sometimes these coordinate may refer to vectors (Force/velocity type, not the data

Answer 1

I've done this sort of thing before. I embed a copy of the base type at the front of the derived type struct. This more closely mimics what c++ might do. Here are two methods I've used.

---

Using simple type:

#define XYZDEF \
    int type; \
    float x; \
    float y; \
    float z

// base type
struct xyzdata {
    XYZDEF;
};

// derived type 1
struct vector {
    XYZDEF;
    int vector_info;
    ...
};

// derived type 2
struct position {
    XYZDEF;
    int position_info;
    ...
};

#define BASEOF(_ptr) \
    ((struct xyzdata *) (_ptr))

// vector_rotate -- rotate a vector
void
vector_rotate(vector *ptr)
{
}

// position_rotate -- rotate a position
void
position_rotate(position *ptr)
{
}

// xyzrotate -- rotate
void
xyzrotate(xyzdata *ptr)
{

    switch (ptr->type) {
    case TYPE_POSITION:
        vector_rotate((vector *) ptr);
        break;
    case TYPE_VECTOR:
        position_rotate((position *) ptr);
        break;
    }
}

---

Using a virtual function table pointer:

#define XYZDEF \
    int type; \
    vtbl *vtbl; \
    float x; \
    float y; \
    float z

// forward definitions
struct xyzdata;
struct vector;
struct position;

// virtual function table
struct vtbl {
    void (*rotate)(struct xyzdata *);
};

// base type
struct xyzdata {
    XYZDEF;
};

// derived type 1
struct vector {
    XYZDEF;
    int vector_info;
    ...
};

// derived type 2
struct position {
    XYZDEF;
    int position_info;
    ...
};

#define BASEOF(_ptr) \
    ((struct xyzdata *) (_ptr))

// vector_rotate -- rotate a vector
void
vector_rotate(struct xyzdata *ptr)
{
    struct vector *vec = (void *) ptr;
    ...
}

// position_rotate -- rotate a position
void
position_rotate(struct xyzdata *ptr)
{
    struct position *pos = (void *) ptr;
    ...
}

// xyzrotate -- rotate
void
xyzrotate(xyzdata *ptr)
{

    ptr->vtbl->rotate(ptr);
}