帮忙分析一段C++代码
刚接触C++，碰到一段代码 ，帮忙看下。谢谢了
#include <iostream>
using namespace std;
class A
{
public:
A()
{
doSth();
}
virtual void doSth()
{
cout<<"I am A"<<endl;
}
};
class B:public A
{
public:
virtual void doSth()
{
cout<<"I am B"<<endl;
}
};
int main()
{
B b;
return 0;
}
