#include <iostream>
using namespace std;
class base
{
public:
base(int i)
{
x=i;
cout<<"constructor of base."<<endl;
}
~base(){cout<<"destructor of base."<<endl;}
viod show(){cout<<"x="<<x<<endl;}
private:
int x;
};
class derived:public base
{

public:
derived(int i):base(i),d(i){cout<<"constructor of derived."<<endl;}
private:
base d;
};
void main()
{
derived obj(5);
obj.show();
}

运行结果：
constructor of base.
constructor of base.//怎么有两遍？不懂
constructor of derived.
x=5
destructor of base.
destructor of base.

derived(int i):base(i),d(i)等于derived(int i):base(i){...}加derived(int i):d(i){...}

derived(int i):base(i),d(i){cout<<"constructor of derived."<<endl;}
这句给X赋了两次值 所以会出现两次cons  结果也出现了两次des

derived(int i):base(i),d(i){cout<<"constructor of derived."<<endl;}
derived(int i):base(i)是子类的构造函数显示调用基类的构造函数，打印一次constructor of base.
d(i) 是derived中的base d进行初始化，所以调用构造函数base(int i) ,又打印一次constructor of base.

回复 楼主 jjg
4楼正解