C / C++ / MFC

unit* LUnits = new unit[2];

LUnits[0] = dynamic_cast<unit*>(S);

unit** LUnits = new unit*[2];

unit** LUnits = new units*[2];  // create an array of pointers to unit
soldier* S = new soldier;
unit[0] = S; // nb we don't need to down cast from soldier to unit

// original class
class C1 {
   int i;
   double d;
public:
   C1(int x, double y) : i(x), d(y) {}
   ...
}; 

// new class :
class C2 {
  int i;
  double d;
  std::string str; // <<= "addition" to C1
public:
  C2(int x, double y, std::string s) : i(x), d(y), str(s){}
  ...
};

// original class
class C1 {
   int i;
   double d;
public:
   C1(int x, double y) : i(x), d(y) {}
   ...
}; 

// new class :
class C2 : public C1 {
  std::string str; // <<= "addition" to C1
public:
  C2(int x, double y, std::string z) :
     C1(x, y), // instantiate the C1 portion of C2
     str(z)    // instantiate new object of C2
  {}
  // add any new functionality needed for a C2 object
};

jana_hus wrote:

immature flaming responses will be as always ignored.

Alex D Aug2024 wrote:

* BIOS registers for graphics modes and other useful things

"BIOS" "graphics modes" PC-dos

Alex D Aug2024 wrote:

Methods to incorporate these registers in C with methods aka inline assembler

struct Unit {
  Unit (int tag) : dog_tag(tag){};
  virtual std::string kind () = 0;
  int dog_tag;
};

struct Soldier : public Unit {
  Soldier (int tag) : Unit(tag) {};
  virtual std::string kind() {return "soldier";};
  float running_speed;
}

struct Sailor : public Unit {
  Sailor (int tag) : Unit(tag) {};
  virtual std::string kind() {return "sailor";}
  int life_jackets;
};

std::vector<Unit*> actors {new Soldier(555), new Sailor(666);};

int main () {
  Unit* u0 = actors[0];
  std::cout << "Actor 0 is a " << u0.kind() " with tag " << u0.dog_tag << std::endl;

   --------          ------------------------------
u0| 0x1234 |------->| pointer to vtable of Soldier |
   --------         |------------------------------|
                    | dog_tag                      |
                    | -----------------------------|
                    | running_speed                |
                     ------------------------------

Soldier *s = (Soldier *)u0;
std::cout << "Running speed " << s->running_speed << std::endl;

Sailor *ss = (Sailor*)u0;
std::cout << "Sailor has " << ss->life_jackets << " life jackets";

Sailor *ss = dynamic_cast<Sailor*>(u0)