指出下列程序中的错误,并说明错误原因。 class X //1 {public: //2 int readme() const {return m;} //3 void writeme(int i) {m=i;} //4 private: //5 int m; //6 }; //7 void f(X& x1,const X& x2) //8 {x1.readme(); //9 x1.writeme(1); //10 x2.readme(); //11 x2.writeme(2); //12 } //13