运算符重载举例

运算符重载的函数一般地采用如下两种形式：成员函数形式和友元函数形式。这两种形式都可访问类中的私有成员。 

　　1. 重载为类的成员函数 

　　这里先举一个关于给复数运算重载复数的四则运算符的例子。复数由实部和虚部构造，可以定义一个复数类，然后再在类中重载复数四则运算的运算符。先看以下源代码： 

#include ＜iostream.h＞  class complex { public: complex() { real=imag=0; } complex(double r, double i) { real = r, imag = i; } complex operator +(const complex &c); complex operator -(const complex &c); complex operator *(const complex &c); complex operator /(const complex &c); friend void print(const complex &c); private: double real, imag; };  inline complex complex::operator +(const complex &c) { return complex(real + c.real, imag + c.imag); }  inline complex complex::operator -(const complex &c) { return complex(real - c.real, imag - c.imag); }  inline complex complex::operator *(const complex &c) { return complex(real * c.real - imag * c.imag, real * c.imag + imag * c.real); }  inline complex complex::operator /(const 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(const complex &c) { if(c.imag＜0) cout＜＜c.real＜＜c.imag＜＜'i'; else cout＜＜c.real＜＜'+'＜＜c.imag＜＜'i'; }  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/c1="; print(c3); cout＜＜endl; }

　　该 程序的运行结果为： 

c1+c2=6+1i c1-c2=-2+5i c1*c2=14+8i c1/c2=0.45+0.8i (c1+c2)*(c1-c2)*c2/c1=9.61538+25.2308i

　　在程序中，类complex定义了4个成员函数作为运算符重载函数。将运算符重载函数说明为类的成员函数格式如下： 

　　＜类名＞ operator ＜运算符＞(＜参数表＞) 

　　其中，operator是定义运算符重载函数的关键字。 

　　程序中出现的表达式： 

　　c1+c2 

　　编译程序将给解释为： 

　　c1.operator+(c2) 

　　其中，c1和c2是complex类的对象。operator+()是运算+的重载函数。 

　　该运算符重载函数仅有一个参数c2。可见，当重载为成员函数时，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，不能再显式说明参数。重载为成员函数时，总时隐含了一个参数，该参数是this指针。this指针是指向调用该成员函数对象的指针。 

　　2. 重载为友元函数 

　　运算符重载函数还可以为友元函数。当重载友元函数时，将没有隐含的参数this指针。这样，对双目运算符，友元函数有2个参数，对单目运算符，友元函数有一个参数。但是，有些运行符不能重载为友元函数，它们是：=,(),[]和-＞。 

　　重载为友元函数的运算符重载函数的定义格式如下： 

　　friend ＜类型说明符＞ operator ＜运算符＞(＜参数表＞)
　　{……} 

　　下面用友元函数代码成员函数，重载编写上述的例子，程序如下： 

#include ＜iostream.h＞  class complex { public: complex() { real=imag=0; } complex(double r, double i) { real = r, imag = i; } friend complex operator +(const complex &c1, const complex &c2); friend complex operator -(const complex &c1, const complex &c2); friend complex operator *(const complex &c1, const complex &c2); friend complex operator /(const complex &c1, const complex &c2); friend  void print(const complex &c); private: double real, imag; };  complex operator +(const complex &c1, const complex &c2) { return complex(c1.real + c2.real, c1.imag + c2.imag); }  complex operator -(const complex &c1, const complex &c2) { return complex(c1.real - c2.real, c1.imag - c2.imag); }  complex operator *(const complex &c1, const complex &c2) { return complex(c1.real * c2.real - c1.imag * c2.imag, c1.real * c2.imag + c1.imag * c2.real); }  complex operator /(const complex &c1, const complex &c2) { return complex((c1.real * c2.real + c1.imag + c2.imag) / (c2.real * c2.real + c2.imag * c2.imag), (c1.imag * c2.real - c1.real * c2.imag) / (c2.real * c2.real + c2.imag * c2.imag)); }  void print(const complex &c) { if(c.imag＜0) cout＜＜c.real＜＜c.imag＜＜'i'; else cout＜＜c.real＜＜'+'＜＜c.imag＜＜'i'; }  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/c1="; print(c3); cout＜＜endl; }

　　该程序的运行结果与上例相同。前面已讲过，对又目运算符，重载为成员函数时，仅一个参数，另一个被隐含；重载为友元函数时，有两个参数，没有隐含参数。因此，程序中出现的 c1+c2 

　　编译程序解释为： 

　　operator+(c1, c2) 

　　调用如下函数，进行求值， 

　　complex operator +(const coplex &c1, const complex &c2)