Question

C++编译错误：'operator <<' is ambiguous

向派生类对象用重载的“<<”,编译是提示错误：'operator <<' is ambiguous。

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#include<iostream.h>

class Building
{
protected:
int cs;
public:
Building(int cs=0);
int getcs();
};

Building::Building(int a)
{
cs=a;
}

int Building::getcs() {return cs;}

class Office:public Building
{
protected:
int mhqs;
public:
Office(int cs=0, int mhqs=0);
int getmhqs();
friend ostream & operator << (ostream &, Office &);
};

Office::Office(int a, int f):Building(a),mhqs(f){}

int Office::getmhqs(){return mhqs;}

ostream & operator << (ostream & output, Office o)
{
output<<"Office:"<<endl;
output<<"层数："<<o.getcs()<<endl;
output<<"灭火器数："<<o.getmhqs()<<endl;
return output;
}

void main()
{
Office cO(10,25);
cout<<cO;
————————————

错误提示：
Compiling...
cpp_05c_class.cpp
F:\sth\cpp05\c2\cpp_05c_class.cpp(46) : error C2593: 'operator <<' is ambiguous
执行 cl.exe 时出错.

cpp_05c_class.obj - 1 error(s), 0 warning(s)

Answer 1

把下面的友元放到类定义里面去

friend ostream & operator << (ostream & output, Office o)
{
output<<"Office:"<<endl;
output<<"层数："<<o.getcs()<<endl;
output<<"灭火器数："<<o.getmhqs()<<endl;
return output;
}