c++ operator重载运算符实例代码，举例说明operator关键字的使用方0法，详细的学习例子。
#include <iostream>
using namespace std;class A{public: A(double _data = 0.0):data(_data){} A& operator = (const A& rhs) { data = rhs.data; return *this; } friend A operator + (const A& lhs,const A& rhs); friend A operator - (const A& lhs,const A& rhs); friend A operator * (const A& lhs,const A& rhs); friend A operator + (const A& lhs,double rhs); friend A operator + (double lhs,const A& rhs); friend A operator * (const A& lhs,double rhs); friend A operator * (double lhs,const A& rhs); friend A operator - (const A& lhs,double rhs); friend A operator - (double lhs,const A& rhs); friend ostream& operator << (ostream& fout,A& a);// A& operator += (const A& rhs);// A& operator -= (const A& rhs);// A& operator *= (const A& rhs); private: double data;};A operator + (const A& lhs,const A& rhs){ A res(0); res.data = lhs.data + rhs.data; return res;}A operator - (const A& lhs,const A& rhs){ A res(0); res.data = lhs.data - rhs.data; return res;}A operator * (const A& lhs,const A& rhs){ A res(0); res.data = lhs.data * rhs.data; return res;} A operator + (const A& lhs,double rhs) { A res(0); res.data = lhs.data + rhs; return res;}A operator + (double lhs,const A& rhs){ A res(0); res.data = lhs + rhs.data; return res;}A operator * (const A& lhs,double rhs){ A res(0); res.data = lhs.data * rhs; return res;}A operator * (double lhs,const A& rhs){ A res(0); res.data = lhs * rhs.data; return res;}A operator - (const A& lhs,double rhs){ A res(0); res.data = lhs.data - rhs; return res; }A operator - (double lhs,const A& rhs){ A res(0); res.data = lhs - rhs.data; return res; } ostream& operator << (ostream& fout,A& a){ fout << a.data ; return fout;}int main(int argc, char* argv[]){ A a(2.3); A b(1.2); A d(3.4); A c; c = a + b + d; c=a+b; c=a+1.0; c=a-b; c=a-1.0; c=a*b; c=a*1.0; cout << c << endl; c=1.0+2.0*a*a-3.0*a*b; cout << c << endl; return 0;}