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Dynamic cast
#include <iostream>
using std::cout; // this file uses std::cout
class Animal
{
public:
Animal():itsAge(1) {
cout << "Animal constructor...\n";
}
virtual ~Animal() {
cout << "Animal destructor...\n";
}
virtual void Speak() const {
cout << "Animal speak!\n";
}
protected:
int itsAge;
};
class Cat: public Animal
{
public:
Cat() {
cout << "Cat constructor...\n";
}
~Cat() {
cout << "Cat destructor...\n";
}
void Speak()const {
cout << "Meow\n";
}
void Miao() const {
cout << "Miao\n";
}
};
class Dog: public Animal
{
public:
Dog() {
cout << "Dog Constructor...\n";
}
~Dog() {
cout << "Dog destructor...\n";
}
void Speak()const {
cout << "Woof!\n";
}
};
int main()
{
const int NumberAnimals = 3;
Animal* animalArray[NumberAnimals];
int i;
animalArray[0] = new Dog;
animalArray[1] = new Cat;
animalArray[2] = new Cat;
for (i=0; i<NumberAnimals; i++)
{
animalArray[i]->Speak();
Cat *pRealCat = dynamic_cast<Cat *> (animalArray[i]);
if (pRealCat)
pRealCat->Miao();
else
cout << "not a cat!\n";
delete animalArray[i];
cout << "\n";
}
return 0;
}Animal constructor...
Dog Constructor...
Animal constructor...
Cat constructor...
Animal constructor...
Cat constructor...
Woof!
not a cat!
Dog destructor...
Animal destructor...
Meow
Miao
Cat destructor...
Animal destructor...
Meow
Miao
Cat destructor...
Animal destructor...
dynamic_cast: Cast from Base * to Base *
#include <iostream>
using namespace std;
class Base {
public:
virtual void f() {
cout << "Inside Base\n";
}
};
class Derived : public Base {
public:
void f() {
cout << "Inside Derived\n";
}
};
int main()
{
Base *bp, b_ob;
Derived *dp, d_ob;
bp = dynamic_cast<Base *> (&b_ob);
if(bp) {
cout << "Cast from Base * to Base * OK.\n";
bp->f();
} else
cout << "Error\n";
cout << endl;
return 0;
}Cast from Base * to Base * OK.
Inside Base
dynamic_cast: Cast from Base * to Derived * (wrong)
#include <iostream>
using namespace std;
class Base {
public:
virtual void f() {
cout << "Inside Base\n";
}
};
class Derived : public Base {
public:
void f() {
cout << "Inside Derived\n";
}
};
int main()
{
Base *bp, b_ob;
Derived *dp, d_ob;
dp = dynamic_cast<Derived *> (&b_ob);
if(dp)
cout << "Error\n";
else
cout << "Cast from Base * to Derived * not OK.\n";
cout << endl;
return 0;
}Cast from Base * to Derived * not OK.
dynamic_cast: Cast from Derived * to Base *
#include <iostream>
using namespace std;
class Base {
public:
virtual void f() {
cout << "Inside Base\n";
}
};
class Derived : public Base {
public:
void f() {
cout << "Inside Derived\n";
}
};
int main()
{
Base *bp, b_ob;
Derived *dp, d_ob;
bp = dynamic_cast<Base *> (&d_ob);
if(bp) {
cout << "Cast from Derived * to Base * OK.\n";
bp->f();
} else
cout << "Error\n";
cout << endl;
return 0;
}Cast from Derived * to Base * OK.
Inside Derived
dynamic_cast: Cast from Derived * to Derived *
#include <iostream>
using namespace std;
class Base {
public:
virtual void f() {
cout << "Inside Base\n";
}
};
class Derived : public Base {
public:
void f() {
cout << "Inside Derived\n";
}
};
int main()
{
Base *bp, b_ob;
Derived *dp, d_ob;
dp = dynamic_cast<Derived *> (&d_ob);
if(dp) {
cout << "Cast from Derived * to Derived * OK.\n";
dp->f();
} else
cout << "Error\n";
cout << endl;
return 0;
}Cast from Derived * to Derived * OK.
Inside Derived
Use dynamic_cast to replace typeid
#include <iostream>
#include <typeinfo>
using namespace std;
class Base {
public:
virtual void f() {}
};
class Derived : public Base {
public:
void derivedOnly() {
cout << "Is a Derived Object.\n";
}
};
int main()
{
Base *bp, b_ob;
Derived *dp, d_ob;
// use typeid
bp = &b_ob;
if(typeid(*bp) == typeid(Derived)) {
dp = (Derived *) bp;
dp->derivedOnly();
}
else
cout << "Cast from Base to Derived failed.\n";
return 0;
}Cast from Base to Derived failed.
