C++运算符重载

双目运算符重载 

• 等号运算符重载如果不自己实现，系统会自己生成一个
• 其他的运算符重载，如果需要使用的话，必须自己实现

class Complex
{
public:
	Complex(int a, int b)
	{
		_a = a;
		_b = b;
	}
	//可以根据需要来选择是否要实现拷贝构造函数，析构函数等
	Complex operator+(const Complex& src)//加号运算符重载，-、*、/、&&、||与这个类似
	{
		int a = _a + src._a;
		int b = _b + src._b;
		return Complex(a, b);
	}
private:
	int _a;
	int _b;
};
int main()
{
	Complex a(1, 2);
	Complex b(2, 3);
	Complex c = a + b;
}

• 输出运算符重载

class Complex
{
public:
	Complex(int a, int b)
	{
		_a = a;
		_b = b;
	}
	Complex operator+(const Complex& src)
	{
		int a = _a + src._a;
		int b = _b + src._b;
		return Complex(a, b);
	}
	friend void operator <<(ostream& out, const Complex& src);
	
private:
	int _a;
	int _b;
};
void operator <<(ostream& out, const Complex& src)
{
	out << src._a << "+" << src._b << "i" << endl;
}

int main()
{
	Complex a(1, 2);
	Complex b(2, 3);
	Complex c = a + b;
	cout << c;
	cout << c << a;//error,? 因为返回值，改进方法如下
	return 0;
}

class Complex
{
public:
	Complex(int a, int b)
	{
		_a = a;
		_b = b;
	}
	Complex operator+(const Complex& src)
	{
		int a = _a + src._a;
		int b = _b + src._b;
		return Complex(a, b);
	}
	friend ostream& operator <<(ostream& out, const Complex& src);
	
private:
	int _a;
	int _b;
};
ostream& operator <<(ostream& out, const Complex& src)
{
	out << src._a << "+" << src._b << "i" << endl;
	return out;
}

int main()
{
	Complex a(1, 2);
	Complex b(2, 3);
	Complex c = a + b;
	cout << c;
	cout << c << a;
	return 0;
}

单目运算符重载

前置++重载

class Complex
{
public:
	Complex(int a, int b)
	{
		_a = a;
		_b = b;
	}
	friend ostream& operator <<(ostream& out, const Complex& src);
	Complex& operator++()
	{
		++_a;
		return *this;
	}
private:
	int _a;
	int _b;
};
ostream& operator <<(ostream& out, const Complex& src)
{
	out << src._a << "+" << src._b << "i" << endl;
	return out;
}

int main()
{
	Complex a(1, 2);
	++a;
	cout << a;
	return 0;
}

后置++重载

class Complex
{
public:
	Complex(int a, int b)
	{
		_a = a;
		_b = b;
	}
	friend ostream& operator <<(ostream& out, const Complex& src);

	Complex operator++(int) //后置++重载与前置++的区别就是后置++的int，int无实质作用
	{
		int tmp = _a;
		_a++;
		return Complex(tmp, _b); //返回的是一个临时对象，所以不能用引用去接收
	}
private:
	int _a;
	int _b;
};
ostream& operator <<(ostream& out, const Complex& src)
{
	out << src._a << "+" << src._b << "i" << endl;
	return out;
}

int main()
{
	Complex a(1, 2);
	Complex b = a++;
	cout << a;
	cout << b;
	return 0;
}