C++第四节课要点摘抄

运算符重载：所谓重载，就是重新赋予新的含义。

不能重载的运算符有 .   ::  .*  ?:   sizeof

 

前置和后置运算符总结

C++中通过一个占位参数来区分前置运算和后置运算 

 

代码实现 +  << 和前置++ 后置++的运算符重载

 #include <iostream>

 

using namespace std;

 

class Complex

{

//friend Complex operator +(Complex &c1,Complex &c2);

friend ostream &operator <<(ostream &out,const Complex &c);

private:

        int m_a;

        int m_b;

 

public:

        Complex();

        Complex(int a,int b);

        void print();

        Complex operator +( Complex &c2);

        Complex operator ++(int);

        Complex &operator ++();

};

 

Complex::Complex()

{

         m_a = 0;

         m_b = 0;

}

 

Complex::Complex(int a,int b)

{

        m_a = a;

        m_b = b;

}

 

/*void Complex::print()

{

        cout << m_a << "+" << m_b << "i" << endl;

}*/

 

/*Complex operator +(Complex &c1,Complex &c2)  //通过全局函数重载

{

        Complex tmp;

        tmp.m_a = c1.m_a + c2.m_a;

        tmp.m_b = c1.m_b + c2.m_b;

 

        return tmp;

}*/

 

Complex Complex::operator +(Complex &c2)

{

        /*Complex tmp;

        tmp.m_a = this->m_a + c2.m_a;

        tmp.m_b = this->m_b + c2.m_b;

 

        return tmp;*/

        this->m_a = this->m_a + c2.m_a;

        this->m_b = this->m_b + c2.m_b;

        return *this;

}

 

ostream &operator <<(ostream &out,const Complex &c)

{

        out << c.m_a << " + " << c.m_b << "i";

        return out;

}

 

Complex Complex::operator ++(int)

{

        Complex tmp = *this;

 

        this->m_a++;

        this->m_b++;

 

        return tmp;

 

}

Complex& Complex::operator ++()

{

        this->m_a++;

        this->m_b++;

 

        return *this;

 

}

 

int main()

{

        Complex c1(1,2);

        Complex c2(3,4);

 

        /*Complex c3 = c1 + c2;

        c3.print();

 

        Complex c4 = c1.operator +(c2);

        c4.print();*/

 

        Complex c3;

        c3 = c1 + c2;

        cout << c3 << endl;

 

        Complex c5;

        c1 + c2 = c5;

        cout << c1 << endl;

 

        Complex c4;

        cout << c4++ << endl;

        cout << ++c4 << endl;

 

return 0;

}

 

 == 和 != 运算符重载

clude <iostream>

 

using namespace std;

 

class Complex

{

private:

        int m_a,m_b;

 

public:

        Complex();

        Complex(int a,int b);

        bool operator ==(Complex &c);

        bool operator !=(Complex &c);

};

 

Complex::Complex()

{

        m_a = 0;

        m_b = 0;

}

 

Complex::Complex(int a,int b)

{

        m_a = a;

        m_b = b;

}

 

bool Complex::operator ==(Complex &c)

{

        if(this->m_a == c.m_a && this->m_b == c.m_b)

        {

                return true;

        }

        else

        {

                return false;

        }

}

 

bool Complex::operator !=(Complex &c)

{

        if(this->m_a != c.m_a || this->m_b != m_b)

        {

                return true;

        }

        else

        {

                return false;

        }

}

 

int main()

{

        Complex c1(1,2);

        Complex c2(1,4);

 

        if(c1  == c2)

        {

                cout << "相等" << endl;

        }

        else

        {

                cout << "不相等" << endl;

        }

 

        if(c1  != c2)

        {

                cout << "不相等" << endl;

        }

        else

        {

                cout << "相等" << endl;

        }

return 0;

}

 

为什么不要重载&& 和 || 运算符

1）&&和||是C++中非常特殊的操作符 

2）&&和||内置实现了短路规则 

3）操作符重载是靠函数重载来完成的 

4）操作数作为函数参数传递 

5）C++的函数参数都会被求值，无法实现短路规则