关于运算符重载函数做为友元函数

请问这段代码哪里有错啊，我参考了几本书都是这样写的，可是ＶＣ６．０怎么通不过呢？


#include <iostream>
using namespace std;

class Complex
{
public:
Complex(){real=0;imag=0;}
Complex(double r,double i){real=r;imag=i;}

friend Complex operator + (Complex &c1,Complex &c2);
void display();
private:
double real;
double imag;
};

Complex operator + (Complex &c1,Complex &c2)
{return Complex(c1.real+c2.real,c1.imag+c2.imag);}

void Complex::display()
{cout<<"("<<real<<","<<imag<<"i)"<<endl;
}

int main()
{
Complex c1(3,4),c2(5,-10),c3;
c3=c1+c2;

cout<<"c1=";c1.display();
cout<<"c2=";c2.display();
cout<<"c1+c2=";c3.display();
return 0;
}

报错：

fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'msc1.cpp', line 1786)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information
Error executing cl.exe.

1.obj - 1 error(s), 0 warning(s)