Status ListInsert_DuL(Dlinklist &L,int i,int e)
{
     Dlinklist s,p;
     if(i<0)return OVERFLOW;
     else
     {
         p=GetElemP_DuL(L,i);
         if(!(p))
             return OVERFLOW;
         s=(DlinkList)malloc(sizeof(DuLNode));
         if(!s)return ERROR;
         s->data=e;
         s->prior=p;s->next=p->next;
         p->next->prior=s;p->next=s;
         return OK;
     }
}为什么s=(DlinkList)malloc(sizeof(DuLNode));显示错误[Error] C:\Users\a\Documents\C-Free\Temp\未命名27.cpp:45: error: `DlinkList' was not declared in this scope