10. 연산자 오버로딩 1

---

출처: 윤성우 열혈강의 C++ 예제코드

---

10.1. 연산자 오버로딩의 이해와 유형

• 멤버함수에서 오버로딩하기

#include <iostream>
using namespace std;

class Point 
{
private:
	int xpos, ypos;
public:
	Point(int x=0, int y=0) : xpos(x), ypos(y)
	{  }
	void ShowPosition() const
	{
		cout<<'['<<xpos<<", "<<ypos<<']'<<endl; 
	}
	Point operator+(const Point &ref)    //operator+라는 이름의 함수
	{
		Point pos(xpos+ref.xpos, ypos+ref.ypos);
		return pos;
	}
};

int main(void)
{
	Point pos1(3, 4);
	Point pos2(10, 20);
	Point pos3=pos1.operator+(pos2);

	pos1.ShowPosition();
	pos2.ShowPosition();
	pos3.ShowPosition();
	return 0;
}

• 전역함수에서 오버로딩하기

#include <iostream>
using namespace std;

class Point
{
private:
	int xpos, ypos;
public:
	Point(int x=0, int y=0) : xpos(x), ypos(y)
	{  }
	void ShowPosition() const
	{
		cout<<'['<<xpos<<", "<<ypos<<']'<<endl; 
	}
	friend Point operator+(const Point &pos1, const Point &pos2);
};

Point operator+(const Point &pos1, const Point &pos2)
{
	Point pos(pos1.xpos+pos2.xpos, pos1.ypos+pos2.ypos);
	return pos;
} 

int main(void)
{
	Point pos1(3, 4);
	Point pos2(10, 20);	
	Point pos3=pos1+pos2;

	pos1.ShowPosition();
	pos2.ShowPosition();
	pos3.ShowPosition();
	return 0;
}

---

10.2. 단항 연산자의 오버로딩

• 증가, 감소 연산자의 오버로딩(전위증가)

#include <iostream>
using namespace std;

class Point 
{
private:
	int xpos, ypos;
public:
	Point(int x=0, int y=0) : xpos(x), ypos(y)
	{  }
	void ShowPosition() const
	{
		cout<<'['<<xpos<<", "<<ypos<<']'<<endl; 
	}
	Point& operator++()
	{
		xpos+=1;
		ypos+=1;
		return *this;
	}
	friend Point& operator--(Point &ref);
};

Point& operator--(Point &ref)
{
	ref.xpos-=1;
	ref.ypos-=1;
	return ref;
}

int main(void)
{
	Point pos(1, 2);
	++pos;
	pos.ShowPosition();
	--pos;
	pos.ShowPosition(); 

	++(++pos);
	pos.ShowPosition();
	--(--pos);
	pos.ShowPosition();
	return 0;
}

• 증가, 감소 연산자의 오버로딩(후위증가)

#include <iostream>
using namespace std;

class Point 
{
private:
	int xpos, ypos;
public:
	Point(int x=0, int y=0) : xpos(x), ypos(y)
	{  }
	void ShowPosition() const
	{
		cout<<'['<<xpos<<", "<<ypos<<']'<<endl; 
	}
	Point& operator++() 
	{
		xpos+=1;
		ypos+=1;
		return *this;
	}
	const Point operator++(int)
	{
		const Point retobj(xpos, ypos);   // const Point retobj(*this);
		xpos+=1;
		ypos+=1;
		return retobj;
	}
	friend Point& operator--(Point &ref);
	friend const Point operator--(Point &ref, int);
};

Point& operator--(Point &ref)
{
	ref.xpos-=1;
	ref.ypos-=1;
	return ref;
}

const Point operator--(Point &ref, int)
{
	const Point retobj(ref);
	ref.xpos-=1;
	ref.ypos-=1;
	return retobj;
}

int main(void)
{
	Point pos(3, 5);
	Point cpy;
	cpy=pos--;
	cpy.ShowPosition();
	pos.ShowPosition();

	cpy=pos++;
	cpy.ShowPosition(); 
	pos.ShowPosition();
	return 0;
}

---

10.3. 교환법칙 문제의 해결

• 교환법칙 충족을 위한 연산자 오버로딩

#include <iostream>
using namespace std;

class Point 
{
private:
	int xpos, ypos;
public:
	Point(int x=0, int y=0) : xpos(x), ypos(y)
	{  }
	void ShowPosition() const
	{
		cout<<'['<<xpos<<", "<<ypos<<']'<<endl; 
	}
	Point operator*(int times) 
	{
		Point pos(xpos*times, ypos*times);
		return pos;
	}
	friend Point operator*(int times, Point & ref);
};

Point operator*(int times, Point & ref)
{
	return ref*times;
}

int main(void)
{
	Point pos(1, 2);
	Point cpy;

	cpy=3*pos;
	cpy.ShowPosition();

	cpy=2*pos*3;
	cpy.ShowPosition();
	return 0;
}

---

10.4. cout, cin 그리고 endl의 정체

• «, » 연산자의 오버로딩

#include <iostream>
using namespace std;

class Point 
{
private:
	int xpos, ypos;
public:
	Point(int x=0, int y=0) : xpos(x), ypos(y)
	{  }
	void ShowPosition() const
	{
		cout<<'['<<xpos<<", "<<ypos<<']'<<endl; 
	}
	friend ostream& operator<<(ostream&, const Point&);
};


ostream& operator<<(ostream& os, const Point& pos)
{
	os<<'['<<pos.xpos<<", "<<pos.ypos<<']'<<endl; 
	return os;
}

int main(void)
{
	Point pos1(1, 3);
	cout<<pos1;
	Point pos2(101, 303);
	cout<<pos2;
	return 0;
}