template<typename T>
class shared_ptr
{
    T *_ptr;
    std::size_t *count;
....
public:
    shared_ptr(T *t=new T):_ptr(t),count(new std::size_t(1){}
....
    ~shared_ptr()
    {
        if(--*count==0)
        {
            //假如本人用的是shared_ptr<vector<string>> str,那么怎么delete _ptr就出错了,这里要怎样才能兼容？
            delete _ptr;               
            delete count;
        }
    }
}