西门子笔试c＋＋编程题

西门子笔试c＋＋编程题一道：

写出程序的output

＃i nclude

class a {

private:

int num;

public:

a() {

cout<<"default constructor"<< endl;

}

~a() {

cout<<"desconstructor"<< endl;

cout< }

a(const a &a){

cout<<"copy constructor"< }

void operator=(const a &a) {

cout<<"overload operator"< }

void setnum(int n) {

num=n;

}

};

void main()

{

a a1;

a a2(a1);

a a3=a1;

a &a4=a1;

a1.setnum(1);

a2.setnum(2);

a3.setnum(3);

a4.setnum(4);

}