Polymorphism/C

This is a programming example for the Polymorphism programming task. If the task description is not listed here, refer back to that page.

<lang c>/* After reading this you may understand */ /* why Bjarne Stroustrup's invented C++ */

1. if defined( _WIN32 ) || defined( MSC_VER )
2. define FN_PTR(x) (& x)
3. else
4. define FN_PTR(x) (x)
5. endif

typedef struct Point {

 int x;
 int y;
 void (*dtor)();   /* virtual */
 void (*print)();  /* virtual */

} Point;

Point* Point_new0() {

 Point* pthis = malloc( sizeof( Point ) );
 memset(pthis, 0, sizeof( Point ) );
 pthis->dtor  = FN_PTR(Point_dtor);
 pthis->print = FN_PTR(Point_print);

}

Point* Point_new1(int x0) {

 Point* pthis = malloc( sizeof( Point ) );
 pthis->x = x0;
 pthis->y = 0;
 pthis->dtor  = FN_PTR(Point_dtor);
 pthis->print = FN_PTR(Point_print);

}

Point* Point_new2(int x0, int y0) {

 Point* pthis = malloc( sizeof( Point ) );
 pthis->x = x0;
 pthis->y = y0;
 pthis->dtor  = FN_PTR(Point_dtor);
 pthis->print = FN_PTR(Point_print);

}

void Point_delete(Point** pthis) {

 if(pthis && *pthis)
 {
   (*pthis)->dtor();
   free(*pthis); *pthis = NULL;
 }

}

Point* Point_copy(Point* p) {

 Point* pthis = malloc( sizeof( Point ) );
 memcpy(pthis, p, sizeof( Point ) );
 pthis->dtor  = FN_PTR(Point_dtor);
 pthis->print = FN_PTR(Point_print);
 return pthis;

}

int Point_getX(Point* pthis) { return pthis->x; } int Point_getY(Point* pthis) { return pthis->y; } int Point_setX(Point* pthis, int x0) { pthis->x = x0; } int Point_setY(Point* pthis, int y0) { pthis->y = y0; } void Point_print() { printf("Point\n"); } void Point_dtor() {}

// Trick: This way Circle.x, Circle.y, Circle.r are available typedef union Circle {

 Point point;
 struct _Circle
 {
   Point point;
   int r;
 };

} Circle;

Circle* Circle_new0() {

 Circle* pthis = malloc( sizeof( Circle ) );
 memset(pthis, 0, sizeof( Circle ) );
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);

}

Circle* Circle_new1(int x0) {

 Circle* pthis = malloc( sizeof( Circle ) );
 pthis->x = x0;
 pthis->y = 0;
 pthis->r = 0;
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);

}

Circle* Circle_new2(int x0, int y0) {

 Circle* pthis = malloc( sizeof( Circle ) );
 pthis->x = x0;
 pthis->y = y0;
 pthis->r = 0;
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);

}

Circle* Circle_new3(int x0, int y0, int r0) {

 Circle* pthis = malloc( sizeof( Circle ) );
 pthis->x = x0;
 pthis->y = y0;
 pthis->r = r0;
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);

}

Circle* Circle_newP0(Point* p) {

 Circle* pthis = malloc( sizeof( Circle ) );
 pthis->x = p->x;
 pthis->y = p->y;
 pthis->r = 0;
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);

}

Circle* Circle_newP1(Point* p, int r0) {

 Circle* pthis = malloc( sizeof( Circle ) );
 pthis->x = p->x;
 pthis->y = p->y;
 pthis->r = r0;
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);

}

void Circle_delete(Circle** pthis) {

 if(pthis && *pthis)
 {
   (*pthis)->dtor();
   free(*pthis); *pthis = NULL;
 }

}

Circle* Circle_copy(Circle* c) {

 Circle* pthis = malloc( sizeof( Circle ) );
 memcpy(pthis, c, sizeof( Circle ) );
 pthis->dtor  = FN_PTR(Circle_dtor);
 pthis->print = FN_PTR(Circle_print);
 return pthis;

}

int Circle_getX(Circle* pthis) { return pthis->x; } int Circle_getY(Circle* pthis) { return pthis->y; } int Circle_getR(Circle* pthis) { return pthis->r; } int Circle_setX(Circle* pthis, int x0) { pthis->x = x0; } int Circle_setY(Circle* pthis, int y0) { pthis->y = y0; } int Circle_setR(Circle* pthis, int r0) { pthis->r = r0; } void Circle_print() { printf("Circle\n"); } void Circle_dtor() {}

int main() {

  Point* p = Point_new0();
  Point* c = (Point*)Circle_new0();
  p->print();
  c->print();     
  return 0;

}</lang>