友元类示例（P134）

#include<iostream>
using namespace std;

class myComplex
{
private:
double real,imag;
public:
myComplex();
myComplex(double r,double i);
friend class oper;
};

myComplex::myComplex()
{
real = 0;
imag = 0;
}

myComplex::myComplex(double r,double i)
{
real = r;
imag = i;
}

class oper
{
public:
myComplex addCom(myComplex c1,myComplex c2);
void outCom(myComplex c);
};

myComplex oper::addCom(myComplex c1,myComplex c2)
{
return myComplex(c1.real + c2.real,c1.imag + c2.imag);
}

void oper::outCom(myComplex c)
{
cout<<"("<<c.real<<","<<c.imag<<")";
}

int main()
{
myComplex c1(1,2),c2(3,4),res;
oper o;
res = o.addCom(c1,c2); //通过友元函数不通过类对象
o.outCom(c1);
cout<<"+";
o.outCom(c2);
cout<<"=";
o.outCom(res);
cout<<endl;
return 0;
}