错在哪儿呀？

class base {

int m;
public:
base(int a):m(a);
int Getx(){return m;}

};

class derived:private base{

public:
derived(int b):m(b){};
};

[解决办法]

C/C++ code

derived(int b):base(b){}; // m 在子类中不可访问