二级C 多态性：运算符重载中的两种形式

文章作者 100test 发表时间 2007:03:10 17:11:46
来源 100Test.Com百考试题网

1•. 重载为类的成员函数：

格式： < 类名 > operator < 运算符 >(< 参数表 >)

例如：利用重载运算符实现复数类对象的算术四则运算。

#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<

｝

说明：①程序中的表达式： c1 c2 ，编译程序将解释 c1.operator (c2)

　　　②当重载成为成员函数时，双目运算符仅有一个参数。对单目运算符，重载为成员函数时，总是隐含了一个　参数，该参数是 this 指针。 This 指针指向调用该成员函数对象的指针。

2、重载为友员函数：

　　当重载友员函数时，将没有隐含的参数 this 指针。这样，对双目运算符，友员函数有２个参数，对单目运算符，友员函数有一个参数。

格式： friend < 类型说明符 >operaotr < 运算符 >(< 参数表 >)

{……..}

例如：重写上例：

#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<

｝

说明： c1 c2 编译程序结实为 operator (c1,c2), 将调用 complex operator (complex &.c1,complex &.c2) 求值。

同理， c1-c2 理解为 operator –(c1,c2), 调用 complex operator –(complex &.c1,complex &.c2) 实现上述表达式的求值。

3 、两种重载形式的比较：