20C++的运算符重载

C++的运算符重载

编译器在做对象运算的时候，会调用对象的运算符重载函数(优先调用成员方法)。如果找不到合适的成员方法，则在全局作用域寻找合适的运算符重载函数.

#include<iostream>
using namespace std;
//复数类
class CComplex
{
private:
	int mreal;
	int mimage;
	//友元函数是为了访问private成员变量，不属于成员函数
	friend CComplex operator+(const CComplex& lhs, const CComplex& rhs);
public:
	CComplex(int real = 0, int image = 0):mreal(real), mimage(image)
	{
		cout << "construct" << endl;
	}
	~CComplex(){}
	CComplex(const CComplex& comp)
	{
		cout << "copy" << endl;
		mreal = comp.mreal, mimage = comp.mimage; 
	}
	CComplex operator+(const CComplex& comp)
	{
		return CComplex(this->mreal + comp.mreal, this->mimage + comp.mimage);
	}
	void show()
	{
		cout << "real" << mreal << "image" << mimage << endl;
	}
};

CComplex operator+(const CComplex& lhs, const CComplex& rhs)
{
	return CComplex(lhs.mreal + rhs.mreal, lhs.mimage + rhs.mimage);
}

int main()
{
	CComplex comp1(10, 10);
	CComplex comp2(20, 20);
	//调用comp1.operator+(comp2) 即加法运算符的重载函数，然后在comp3初始化的基础上赋值，而非拷贝构造
	CComplex comp3 = comp1 + comp2; 
	comp3.show();
	//下一行的逻辑是：comp3后跟+，意味着调用CComplex operator+，然后可以注意到，这一行发生了两次构造，其中20->CComplex(20)，即强制类型转换，最后执行operator+
	CComplex comp4 = comp3 + 20; 
	comp4.show();
	//下一行20不会调用CComplex operator+，转而寻找全局作用域下的运算符重载函数，但没有合适的，于是定义了全局的友元运算符重载函数CComplex operator+
	CComplex comp5 = 20 + comp3;
	comp5.show();
	return 0;
}

单目运算符的重载

• operator++()代表前置++
• 其重载形式operator++(int)代表后置++
• 为了统一所有类型对象的输出，可以采用在其类中重载输入输出运算符的形式

#include<iostream>
using namespace std;
//复数类
class CComplex
{
private:
	int mreal;
	int mimage;
	//友元函数是为了访问private成员变量，不属于成员函数
	friend CComplex operator+(const CComplex& lhs, const CComplex& rhs);
	friend ostream& operator<<(ostream& out, const CComplex& src);
	friend istream& operator>>(istream& in, CComplex& src);
public:
	CComplex(int real = 0, int image = 0):mreal(real), mimage(image)
	{
		cout << "construct" << endl;
	}
	~CComplex(){}
	CComplex(const CComplex& comp)
	{
		cout << "copy" << endl;
		mreal = comp.mreal, mimage = comp.mimage; 
	}
	CComplex operator+(const CComplex& comp)
	{
		return CComplex(this->mreal + comp.mreal, this->mimage + comp.mimage);
	}
	CComplex operator++()
	{
		//++this->mimage, ++this->mreal;
		//return *this;
		return CComplex(++mreal, ++mimage);
	}
	CComplex operator++(int)
	{
		/*CComplex comp = *this;
		++this->mimage, ++this->mreal;
		return comp;*/
		return CComplex(mreal++, mimage++);
	}
	void operator+=(const CComplex& comp)
	{
		mreal += comp.mreal;
		mimage += comp.mimage;
	}
	void show()
	{
		cout << "real" << mreal << "image" << mimage << endl;
	}
};

CComplex operator+(const CComplex& lhs, const CComplex& rhs)
{
	return CComplex(lhs.mreal + rhs.mreal, lhs.mimage + rhs.mimage);
}
ostream& operator<<(ostream &out, const CComplex& src)//提供输出符号的重载形式
{
	out << "real:" << src.mreal << "image:" << src.mimage;
	return out;
}
istream& operator>>(istream& in, CComplex& src)//提供输入符号的重载形式
{
	in >> src.mreal >> src.mimage;
	return in;
}

int main()
{
	CComplex comp1(10, 10);
	CComplex comp2 = comp1++;
	CComplex comp3 = ++comp1;
	comp1.show();
	comp2.show();
	comp3.show();
	comp1 += comp1;
	comp1.show();
	cout << comp1 << endl;
	cin >> comp1 >> comp2;
	cout << comp1 << endl << comp2 << endl;
	return 0;
}