二級C++多態(tài)性：運(yùn)算符重載中的兩種形式

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1• 重載為類的成員函數(shù)：
    格式： < 類名 > operator < 運(yùn)算符 >(< 參數(shù)表 >)
    例如：利用重載運(yùn)算符實現(xiàn)復(fù)數(shù)類對象的算術(shù)四則運(yùn)算。
    #include
    class complex
    {
    public:
    complex(){ real=imag=0;}
    complex(double r,double I)
    {
    real=r;imag=I;
    }
    complex operator +(complex &c);
    complex operator -(complex &c);
    complex operator *(complex &c);
    complex operator /(complex &c);
    friend void print(complex &c);
    private:
    double real,imag;
    };
    inline complex complex::operator +(complex &c)
    {
    return complex(real+c.real,imag+c.imag);
    }
    inline complex complex::operator –(complex &c)
    {
    return complex(real-c.real,imag-c.imag);
    }
    inline complex complex::operator *(complex &c)
    {
    return complex(real*c.real-imag*c.imag,real*c.imag+imag*c.real);
    }
    inline complex complex::operator /(complex &c)
    {
    return complex((real*c.real+imag*c.imag)/(c.real*c.real+c.imag*c.imag),
    (imag*c.real-real*c.imag)/(c.real*c.real+c.imag*c.imag));
    }
    void print(complex &c)
    {
    if(c.imag<0)
    cout<    else
    cout<    }
    void main()
    {
    complex c1(2.0,3.0),c2(4.0,-2.0),c3;
    c3=c1+c2;
    cout<<”\nc1+c2=”;
    print(c3);
    c3=c1-c2;
    cout<<”\nc1-c2=”;
    print(c3);
    c3=c1*c2;
    cout<<”\nc1*c2=”;
    print(c3);
    c3=c1/c2;
    cout<<”\nc1/c2=”;
    print(c3);
    c3=(c1+c2)*(c1-c2)*c2/c1;
    cout<<”\n(c1+c2)*(c1-c2)*c2/c 1” ;
    print(c3);
    cout<    ｝
    說明：①程序中的表達(dá)式： c1+c2 ，編譯程序?qū)⒔忉?c1.operator+(c2)
    ②當(dāng)重載成為成員函數(shù)時，雙目運(yùn)算符僅有一個參數(shù)。對單目運(yùn)算符，重載為成員函數(shù)時，總是隱含了一個　參數(shù)，該參數(shù)是 this 指針。 This 指針指向調(diào)用該成員函數(shù)對象的指針。
    2、重載為友員函數(shù)：
    當(dāng)重載友員函數(shù)時，將沒有隱含的參數(shù) this 指針。這樣，對雙目運(yùn)算符，友員函數(shù)有２個參數(shù)，對單目運(yùn)算符，友員函數(shù)有一個參數(shù)。
    格式： friend < 類型說明符 >operaotr < 運(yùn)算符 >(< 參數(shù)表 >)
    {……..}
    例如：重寫上例：
    #include
    class complex
    {
    public:
    complex (){real=imag=0;}
    complex(double r,double I)
    {
    real=r;imag=I;
    }
    friend complex operator +(complex &c1,complex &c2);
    friend complex operator -(complex &c1,complex &c2);
    friend complex operator *(complex &c1,complex &c2);
    friend complex operator /(complex &c1,complex &c2);
    friend void print(complex &c);
    private:
    double real,imag;
    };
    complex operator +(complex &c1,complex &c2)
    {
    return complex(c1real+c2.real,c1.imag+c2.imag);
    }
    complex operator –(complex &c1,complex &c2)
    {
    return complex(c1.real-c2.real,c1.imag-c2.imag);
    }
    complex operator *(complex &c1,complex &c2)
    {
    return complex(c1real*c2.real-c1.imag*c2.imag,c1.real*c2.imag+c1.imag*c2.real);
    }
    complex operator /(complex &c1,complex &c2)
    {
    return complex((c1.real*c2.real+c1.imag*c2.imag)/(c1.real*c2.real+c1.imag*c2.imag),
    (c1.imag*c2.real-c1.real*c2.imag)/(c1.real*c2.real+c1.imag*c2.imag));
    }
    void print(complex &c)
    {
    if(c.imag<0)
    cout<    else
    cout<    }
    void main()
    {
    complex c1(2.0,3.0),c2(4.0,-2.0),c3;
    c3=c1+c2;
    cout<<”\nc1+c2=”;
    print(c3);
    c3=c1-c2;
    cout<<”\nc1-c2=”;
    print(c3);
    c3=c1*c2;
    cout<<”\nc1*c2=”;
    print(c3);
    c3=c1/c2;
    cout<<”\nc1/c2=”;
    print(c3);
    c3=(c1+c2)*(c1-c2)*c2/c1;
    cout<<”\n(c1+c2)*(c1-c2)*c2/c 1” ;
    print(c3);
    cout<    ｝
    說明： c1+c2 編譯程序結(jié)實為 operator+(c1,c2), 將調(diào)用 complex operator +(complex &c1,complex &c2) 求值。
    同理， c1-c2 理解為 operator –(c1,c2), 調(diào)用 complex operator –(complex &c1,complex &c2) 實現(xiàn)上述表達(dá)式的求值。