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

You can use a union for this. Your main struct would contain a union of the "derived" structs as well as a "flag" field telling you which member of the union is valid:

enum { DERIVED11, DERIVED2, DERIVED3 };

struct derived1 { int x1; };
struct derived2 { char x2; };
struct derived3 { float x3; };

struct ThreeDCartesianData
{
   float x;
   float y;
   float z;
   int derivedType;
   union {
     struct derived1 d1;
     struct derived2 d2;
     struct derived3 d3;
   } derived;
};

Then you can use them like this:

struct ThreeDCartesianData data1;
data1.x=0;
data1.y=0;
data1.z=0;
data1.derivedType = DERIVED1;
data1.derived.d1.x1 = 4;

You could alternately define them like this:

struct common
{
   int type;
   float x;
   float y;
   float z;
};
struct derived1
{
   int type;
   float x;
   float y;
   float z;
   int x1;
};
struct derived2
{
   int type;
   float x;
   float y;
   float z;
   char x2;
};
struct derived3
{
   int type;
   float x;
   float y;
   float z;
   float x3;
};

union ThreeDCartesianData {
     struct common c;
     struct derived1 d1;
     struct derived2 d2;
     struct derived3 d3;
};    

And use them like this:

union ThreeDCartesianData data1;
data1.c.type=DERIVED1;
data1.d1.x=0;
data1.d1.y=0;
data1.d1.z=0;
data1.d1.x1 = 4;

If all the structs in a union have an initial list elements of the same type in the same order, the standard allows you to access those fields from any of the sub-structs safely.