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

What about using typedefs?

typedef struct general3d {
    float x;
    float y;
    float z;
} general3d_t;

typedef general3d position;
typedef general3d velocity;

This way, when you come across something that's a velocity type, you encode that into the variable type, but under the hood, it's still just 3 points, x, y, z. Then, readers of the code will know you're talking about a velocity and not a position. If you want to get really crazy with it, you hide general3d away in some implementation file, so a user can never instantiate a general3d on their own, since they should be using either position or velocity as the situation requires; this may or may not be reasonable for your task at hand/worth the extra effort.

EDIT: I'm not positive about variable-renaming or about adding more variables directly to the same struct, but I would start to head in the direction of a different design at that point.

On the one hand, if you have two structs that have the same underlying types but require different names, you probably just have two separate structs. For example:

struct point3d {
    float x;
    float y;
    float z;
};

struct person {
    float age;
    float weight;
    float salary;
};

Yes, those are both 3 floats, but their understanding is very different, and they should be able to vary on their own if one or the other changes. Perhaps I want to add a name field to the person, but there's no reasonable analogue for a char * on point3d. Just define them separately if they mean different things.

As for adding more variables, that sounds like structs that contain other structs:

struct point3d {
    float x;
    float y;
    float z;
};

struct person {
    point3d position;
    float age;
    float weight;
    float salary;
};

// access like:
person.position.x;