16. C++의 형 변환 연산자

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출처: 윤성우 열혈강의 C++ 예제코드

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16.1. C++에서의 형 변환 연산

• dynamic_cast: 상속관계에서 안전한 형 변환

#include <iostream>
using namespace std;

class Car
{
private:
	int fuelGauge;		
public:
	Car(int fuel) : fuelGauge(fuel)
	{  }
	void ShowCarState()
	{
		cout<<"잔여 연료량: "<<fuelGauge<<endl;
	}
};

class Truck : public Car
{
private:
	int freightWeight;

public:
	Truck(int fuel, int weight)
		: Car(fuel), freightWeight(weight)
	{  }
	void ShowTruckState()
	{
		ShowCarState();
		cout<<"화물의 무게: "<<freightWeight<<endl;
	}
};

int main(void)
{
	Car * pcar1=new Truck(80, 200);
	Truck * ptruck1=dynamic_cast<Truck*>(pcar1);     // 컴파일 에러

	Car * pcar2=new Car(120);
	Truck * ptruck2=dynamic_cast<Truck*>(pcar2);     // 컴파일 에러

	Truck * ptruck3=new Truck(70, 150);
	Car * pcar3=dynamic_cast<Car*>(ptruck3);     // 컴파일 OK!

	return 0;
}

• static_cast: A 타입에서 B타입으로

#include <iostream>
using namespace std;

class Car
{
private:
	int fuelGauge;		
public:
	Car(int fuel) : fuelGauge(fuel)
	{  }
	void ShowCarState()
	{
		cout<<"잔여 연료량: "<<fuelGauge<<endl;
	}
};

class Truck : public Car
{
private:
	int freightWeight;

public:
	Truck(int fuel, int weight)
		: Car(fuel), freightWeight(weight)
	{  }
	void ShowTruckState()
	{
		ShowCarState();
		cout<<"화물의 무게: "<<freightWeight<<endl;
	}
};

int main(void)
{
	Car * pcar1=new Truck(80, 200);
	Truck * ptruck1=static_cast<Truck*>(pcar1);     // 컴파일 OK!
	ptruck1->ShowTruckState();
	cout<<endl;

	Car * pcar2=new Car(120);
	Truck * ptruck2=static_cast<Truck*>(pcar2);     // 컴파일 OK! 그러나!
	ptruck2->ShowTruckState();
	return 0;
}

• const_cast: const의 성향을 삭제

#include <iostream>
using namespace std;

void ShowString(char* str)
{
	cout<<str<<endl;
}

void ShowAddResult(int& n1, int& n2)
{
	cout<<n1+n2<<endl;
}

int main(void)
{
	const char * name="Lee Sung Ju";
	ShowString(const_cast<char*>(name));

	const int& num1=100;
	const int& num2=200;
	ShowAddResult(const_cast<int&>(num1), const_cast<int&>(num2));
	return 0;
}

• reinterpret_cast: 상관없는 자료형으로 형 변환

#include <iostream>
using namespace std;

int main(void)
{
	int num=0x010203;
	char * ptr=reinterpret_cast<char*>(&num);

	for(int i=0; i<sizeof(num); i++)
		cout<<static_cast<int>(*(ptr+i))<<endl;

	return 0;
}