Visual C++ - dynamic_cast
By extending example in the previous section of static cast, Shape is the base class. Circle, Square, Rectangle are the 3 classes dervied from the base class Shape. static_cast can be used to resolve ambiguity arises because of implicit casting by explictly specifying the data type while casting.
1. The object p1 initialization uses the C Style casting
2. The object p2 initialization uses implicit casting
3. The object p3 initialization uses using static_cast.
All the 3 pointer objects p1, p2, p3 are converted back to Circle pointer using dynamic_cast. Actually only the pointer p2 is a pointer to Circle object. The outcome would p1 and p3 will get the NULL value and p2 will get the pointer to Circle Object. This casting requires RTTI (Run-Time Type Information) to be enabled.
Source Code
class Shape
{
public:
Shape()
{
std::cout << "Shape\n";
}
virtual void draw() = 0; // pure virtual function
};
class Rect1 : public Shape
{
int l,b;
public:
Rect1()
{
std::cout << "Rectangle\n\n";
}
virtual void draw()
{
std::cout << "Drawing Rectangle\n\n";
}
};
class Circle : public Shape
{
int r;
public:
Circle()
{
std::cout << "Circle\n\n";
}
virtual void draw()
{
std::cout << "Drawing Circle\n\n";
}
};
class Square : public Shape
{
int a;
public:
Square()
{
std::cout << "Square\n\n";
}
virtual void draw()
{
std::cout << "Drawing Square\n\n";
}
};
int _tmain(int argc, _TCHAR* argv[])
{
Shape *p1 = (Shape*) (new Rect1()); // C Style Casting equal to static_cast
Shape *p2 = new Circle(); // Implict cast
Shape *p3 = static_cast (new Square()); // static_cast
Circle* c1 = dynamic_cast(p1);
Circle* c2 = dynamic_cast(p2);
Circle* c3 = dynamic_cast(p3);
if(c1 == NULL)
std::cout << "c1 is not a pointer to Circle\n";
else
std::cout << "c1 is a pointer to Circle\n";
if(c2 == NULL)
std::cout << "c2 is not a pointer to Circle\n";
else
std::cout << "c2 is a pointer to Circle\n";
if(c3 == NULL)
std::cout << "c3 is not a pointer to Circle\n\n";
else
std::cout << "c3 is a pointer to Circle\n\n";
return 0;
}
Output
Shape
Rectangle
Shape
Circle
Shape
Square
c1 is not a pointer to Circle
c2 is a pointer to Circle
c3 is not a pointer to Circle
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