书上不是说友元函数可以访问类的私有成员嘛..可是我的程序为什么出错了...denom,numer是类的私有成员
friend ostream & operator << (ostream & out,const Rational & value){
    if(value.denom!=0){
        out<<value.numer;
        if(value.denom!=1){
            out<<'/'<<value.denom;
            return out;
        }

        if(value.numer==0)
            out<<"indeterminate";
        else{
            if(value.numer<=0)
                out<<'-';
            out<<"infinity";
        }
        return out;
    }
}



error C2248: 'denom' : cannot access private member declared in class 'Rational'
        e:\programmer\visual c++\rationals\rational.h(20) : see declaration of 'denom'
E:\programmer\Visual C++\Rationals\Rational.cpp(94) : error C2248: 'numer' : cannot access private member declared in class 'Rational'
        e:\programmer\visual c++\rationals\rational.h(19) : see declaration of 'numer'
E:\programmer\Visual C++\Rationals\Rational.cpp(95) : error C2248: 'denom' : cannot access private member declared in class 'Rational'
        e:\programmer\visual c++\rationals\rational.h(20) : see declaration of 'denom'
E:\programmer\Visual C++\Rationals\Rational.cpp(96) : error C2248: 'denom' : cannot access private member declared in class 'Rational'
        e:\programmer\visual c++\rationals\rational.h(20) : see declaration of 'denom'
E:\programmer\Visual C++\Rationals\Rational.cpp(100) : error C2248: 'numer' : cannot access private member declared in class 'Rational'
        e:\programmer\visual c++\rationals\rational.h(19) : see declaration of 'numer'
E:\programmer\Visual C++\Rationals\Rational.cpp(103) : error C2248: 'numer' : cannot access private member declared in class 'Rational'
        e:\programmer\visual c++\rationals\rational.h(19) : see declaration of 'numer'
Error executing cl.exe.

友元不是在外部定义的！
要在类内部声明友元函数，在外面定义该全局函数！
看c++的书吧