下面程序的运行结果是 #include<iostream.h> class base{ protected: int a; public: base(){cout <<'0';} }; class basel:virtual base{ public: basel () {cout <<'1';} }; class base2:virtual base{ public: base2(){cout <<'2';} }; class derived:public basel,public base2{ public: derived(){cout <<'3';} }; void main() { derived obj; cout <<end1; }