zhiyinjixu总结：复制构造函数的用法

#include <iostream>
using namespace std;

class A
{
public:
 A()
 { 
 }
 A(A& e)
 {
    x = e.x ;
 }
 int x;
};

int main ()
{
 A ob1;
 ob1.x = 4;
 A ob2(ob1);
 cout<<ob2.x<<endl;
}