Question

c++中的运算符重载operator<<(ostream &os,FUN f)问题,其中FUN是一个类。

请问要怎么样，程序输出的结果才是：*****12345 54321***** ?
程序如下：

#include <iostream>
#include <iomanip>
using namespace std;
class FUN {
friend ostream operator<<(ostream&,FUN);
}fun;
ostream operator<<(ostream& os,FUN f) {
os.setf(ios_base::left);
return os;
}
void main() {
cout<<setfill('*')<<setw(10)<<12345<<" ";
cout<<fun<<setw(10)<<54321<<endl; // error C2593: 'operator <<' is ambiguous
}
请高手帮我改一下。

Answer 1

#include <iostream>
#include <iomanip>

using namespace std;
class FUN {
friend ostream& operator<<(ostream&,FUN&);
}fun;

ostream& operator<<(ostream& os,FUN& f) {
os.setf(ios_base::left);
return os;
}
void main() {

cout<<setfill('*')<<setw(10)<<12345<<" ";
cout<<fun<<setw(10)<<54321<<endl; // error C2593: 'operator <<' is ambiguous
}
//operator<<中的FUN最好是FUN&。返回值必须是ostream&，而不是ostream

Answer 2

传值传址的问题，用引用吧！
#include <iostream>
#include <iomanip>
using namespace std;

class FUN
{
friend ostream& operator << (ostream&,FUN&);
}fun;

ostream& operator<<(ostream& os,FUN& f)
{
os.setf(ios_base::left);
return os;
}

void main()
{
cout<<setfill('*')<<setw(10)<<12345<<" ";
cout<<fun<<setw(10)<<54321<<endl;
}

Answer 3

我这里没报错。爱莫能助= = =