Question

error C2593: 'operator <<' is ambiguous 执行 cl.exe 时出错.

#include<iostream>
using namespace std;
class A
{
public:
A(int a,int b):x(a),y(b){}
friend ostream &operator << (ostream&, const A&);
int x;
int y;
};
ostream &operator << (ostream &output, const A &p)
{
output<<"("<<p.x<<","<<p.y<<")"<<endl;
return output;
}
int main()
{
A a(1,2);
cout<<a;
return 0;
}

Answer 1

#include<iostream.h>
class A
{
public:
A(int a,int b):x(a),y(b){}
friend ostream &operator << (ostream&, const A&);
int x;
int y;
};
ostream &operator << (ostream &output, const A &p)
{
output<<"("<<p.x<<","<<p.y<<")"<<endl;
return output;
}
int main()
{
A a(1,2);
cout<<a;
return 0;
}

友元函数是不能用using namespace std;
得用<iostream.h>

Answer 2

程序没错，可能你编译器的问题