C++中的运算符重载详解

class Complex
{
private:
    double Real,Image;
public:
    Complex():Real(0),Image(0)  {}
    Complex(double r, double i) : Real(r),Image(i) {}
    ~Complex()  {}
};

int main()
{
    Complex c1(1.2,2.3);
    Complex c2(45,56);

    Complex c3;
    c3 = c1.Add(c2);        
   
}

Complex::Complex Add(const Complex &c)
{
    Complex co;
    co.Real = this->Real + c.Real;
    co.Image = this->Image + c.Image;
    return co;
}

Complex::Complex Add(const Complex &c) const	
{
    return Complex(c.Real + this->Real, c.Image + this.Image);
}

Complex::Complex &Add(const Complex &c) const	
{
    return Complex(c.Real + this->Real, c.Image + this.Image);
}

//Complex::Complex Add(const Complex &c) const
Complex::Complex +(const Complex &c) const 
{
	Complex co;
	co.Real = this->Real + c.Real;
	co.Image = this->Image + c.Image;
	return co;
}

int main()
{
    ...
    //c3 = c1.Add(c2);  
    c3 = c1.+(c2);    //将原先Add的地方改变为加号。
    ...
}
	        

Complex operator+(const Complex &c) const 
{
     return Complex(c.Real + this->Real,c.Image + this->Image);
}

int main()
{
     Complex c1(1.2,2.3);
     Complex c2(10,10);
     Complex c3;
     c3 = c1 + c2;
    
     //上面一行实际上是
     //c3 = c1.operator+ (c2);
     //c3 = operator+(&c1,c2);  //编译器还会经过一次编译
}

class Object
{
public:
    Object()    {}							//构造函数
    ~Object()   {}							//析构函数
    Object(const Object &obj)   {}			//拷贝构造函数
    Object &operator=() {const Object &obj} //赋值函数
    {
        return *this;
    }
    
    Object *operator&()						//普通对象的&（取地址符）的重载
    {
        return this;
    }
    
    const Object *operator&() const			//常对象的&（取地址符）重载
    {
        return this;
    }

};

class Object
{
    int value;
public:
    Object ()   {
        cout << "create:" << this << endl;
    }                  //普通构造函数
    Object (int x = 0):value(x) {cout << "create:" << this << endl;}  //缺省构造函数
    ~Object()                       //析构函数
    {
        cout << "~Objcet() " << this << endl;
    }
    Object(Object &obj):value(obj.value)             
    {
        cout << "Copy create:" << this << endl;
    }

    int & Value()
    {
        return value;
    }

    const int &Value() const 
    {
        return value;
    }  
       
     Object &operator=(const Object& obj)        //此处加引用
    {
        this->value = obj.value;
        return *this;       //this指针指向objb的地址。赋值函数结束后，objb不会被消亡，所以可以以引用返回
    }
    
	void operator=(const Object& obj)       //赋值语句不可给this指针加const
    {
        this->value = obj.value;
    }
    
};

int main()
{
    Object objx(0);
    Object objy(0);
    objy = fun(objx);
    cout << objy.Value() << endl;
    return 0;
}

obja = objb = objc;

//当调用等号运算符函数的时候。
obja = objb.operator = (objc);
obja = operator = (&objb,objc);
//如果此处是调用的是 void operator=(const Object& obj) ；
//等号从右向左指向，我们不能把一个void 类型赋给一个obja对象类型。

Object &operator=(const Object& obj)        //此处加引用
{
	this->value = obj.value;
	return *this;       //this指针指向objb的地址。赋值函数结束后，objb不会被消亡，所以可以以引用返回
}

obja.operator=(operator=(&objb,objc));
operator=(&obja,operator=(&objb,objc));

Object &operator=(const Object &obj)
{
    if(this != &obj)
    {
        this->value = obj.value
    }
}

> 问题7：如果遇到obja = obja这种情况，如何赋值呢？
>
> 回答：对this指针和形参引用进行判断。

```cpp
Object &operator=(const Object &obj)
{
    if(this != &obj)
    {
        this->value = obj.value
    }
}