c++使用嵌套类实现堆栈

class CStack
{
private:
Struct CItem
{
CBox* pBox;
CItem* pNext;

CItem(CBox* pB,CItem* pN):pBox(pB),pNext(pN){}
};
public:
void Push(CBox* pBox)
{
ptop = new CItem(pBox,pTop);
}
CBox* Pop()
{
if(pTop == 0)
return 0;

CBox* pBox = pTop->pBox;
CItem* pTemp = pTop;
pTop = pTop->Next;
delete pTemp;
retuen pBox;
}
}