Mega Code Archive
Demonstrate runtime type id
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#include <iostream>
#include <cstdlib>
using namespace std;
class two_d_shape {
protected:
double x, y;
public:
two_d_shape(double i, double j) {
x = i;
y = j;
}
double getx() { return x; }
double gety() { return y; }
virtual double area() = 0;
};
// Create a subclass of two_d_shape for triangles.
class triangle : public two_d_shape {
public:
triangle(double i, double j) : two_d_shape(i, j) { }
double area() {
return x * 0.5 * y;
}
};
// Create a subclass of two_d_shape for rectangles.
class rectangle : public two_d_shape {
public:
rectangle(double i, double j) : two_d_shape(i, j) { }
double area() {
return x * y;
}
};
// Create a subclass of two_d_shape for circles.
class circle : public two_d_shape {
public:
circle(double i, double j=0) : two_d_shape(i, j) { }
double area() {
return 3.14 * x * x;
}
};
// A factory for objects derived from two_d_shape.
two_d_shape *factory() {
static double i = (rand() % 100) / 3.0, j = (rand() % 100) / 3.0;
i += rand() % 10;
j += rand() % 12;
cout << "Generating object.\n";
switch(rand() % 3 ) {
case 0: return new circle(i);
case 1: return new triangle(i, j);
case 2: return new rectangle(i, j);
}
return 0;
}
// Compare two shapes for equality. This means that their
// types and dimensions must be the same.
bool sameshape(two_d_shape *alpha, two_d_shape *beta) {
cout << "Comparing a " << typeid(*alpha).name()
<< " object to a " << typeid(*beta).name()
<< " object\n";
if(typeid(*alpha) != typeid(*beta)) return false;
if(alpha->getx() != beta->getx() &&
alpha->gety() != beta->gety()) return false;
return true;
}
int main()
{
// Create a base class pointer to two_d_shape.
two_d_shape *p;
// Generate two_d_shape objects.
for(int i=0; i < 6; i++) {
// Generate an object.
p = factory();
// Display the name of the object.
cout << "Object is " << typeid(*p).name() << endl;
// Display its area.
cout << " Area is " << p->area() << endl;
// Keep a count of the object types that have been generated.
if(typeid(*p) == typeid(triangle))
cout << " Base is " << p->getx() << " Height is "
<< p->gety() << endl;
else if(typeid(*p) == typeid(rectangle))
cout << " Length is " << p->getx() << " Height is "
<< p->gety() << endl;
else if(typeid(*p) == typeid(circle))
cout << " Diameter is " << p->getx() << endl;
cout << endl;
}
cout << endl;
// Make some objects to compare.
triangle t(2, 3);
triangle t2(2, 3);
triangle t3(3, 2);
rectangle r(2, 3);
// Compare two two_d_objects.
if(sameshape(&t, &t2))
cout << "t and t2 are the same.\n";
if(!sameshape(&t, &t3))
cout << "t and t3 differ.\n";
if(!sameshape(&t, &r))
cout << "t and r differ.\n";
cout << endl;
return 0;
}
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