ns2中宏定义实现的链表LIST

ns2中链表的定义在/ns-allinone-2.35/ns2.35/lib/bsd-list.h中。

学习的协议为AOMDV，链表的具体使用在aomdv.h中。

-----------------------------------------------------------链表的定义-----------------------------------------------------------

List的定义：

#define LIST_HEAD(name, type)						\
struct name {								\
	type *lh_first;	/* first element */			\
}

#define LIST_ENTRY(type)						\
struct {								\
	type *le_next;	/* next element */			\
	type **le_prev;	/* address of previous next element */	\
}

使用结构体定义链表，参数name规定了链表明，type定义了元素的类型。LIST_ENTRY中的成员le_prev，它不是平时双向链表中的前向指针(指向前一个元素)，而是前向前一个元素的le_next成员的指针。le_prev指向的是指针的地址，而不是元素的地址。

aomdv.h中的class AOMDV_Route定义了构造函数：

AOMDV_Route(nsaddr_t nexthop, nsaddr_t lasthop=0) {
				nh_addr = nexthop;
				lh_addr = lasthop;
		  }

之后使用LIST_ENTRY和LIST_HEAD构造了链表元素route_link，链表头为aomdv_routes：

LIST_ENTRY(AOMDV_Route) route_link;
LIST_HEAD(aomdv_routes, AOMDV_Route);

---------------------------------------------------------链表的插入/删除----------------------------------------------------------

List Function:

#define	LIST_INIT(head) {						\
	(head)->lh_first = NULL;					\
}

#define LIST_INSERT_AFTER(listelm, elm, field) {			\
	if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)	\
		(listelm)->field.le_next->field.le_prev =		\
		    &(elm)->field.le_next;				\
	(listelm)->field.le_next = (elm);				\
	(elm)->field.le_prev = &(listelm)->field.le_next;		\
}

#define LIST_INSERT_BEFORE(listelm, elm, field) {			\
	(elm)->field.le_prev = (listelm)->field.le_prev;		\
	(elm)->field.le_next = (listelm);				\
	*(listelm)->field.le_prev = (elm);				\
	(listelm)->field.le_prev = &(elm)->field.le_next;		\
}

#define LIST_INSERT_HEAD(head, elm, field) {				\
	if (((elm)->field.le_next = (head)->lh_first) != NULL)		\
		(head)->lh_first->field.le_prev = &(elm)->field.le_next;\
	(head)->lh_first = (elm);					\
	(elm)->field.le_prev = &(head)->lh_first;			\
}

#define LIST_REMOVE(elm, field) {					\
	if ((elm)->field.le_next != NULL)				\
		(elm)->field.le_next->field.le_prev = 			\
		    (elm)->field.le_prev;				\
	*(elm)->field.le_prev = (elm)->field.le_next;			\
}

aomdv.h中的class AOMDVBroadcastID定义了aomdv_routes类型的后向链表reverse_path_list和前向链表forward_path_list：

aomdv_routes     reverse_path_list;     // List of reverse paths used for forwarding replies
aomdv_routes     forward_path_list;     // List of forward paths advertised already

在类AOMDVBroadcastID的构造函数中初始化链表：

        AOMDVBroadcastID(nsaddr_t i, u_int32_t b) { 
				src = i; 
				id = b;  
				// AOMDV code
				count=0;  
				LIST_INIT(&reverse_path_list);
				LIST_INIT(&forward_path_list);
        }

在类AOMDVBroadcastID的成员函数reverse_path_insert()中将元素插入链表中。（前向链表类似）

        inline AOMDV_Route* reverse_path_insert(nsaddr_t nexthop, nsaddr_t lasthop=0) {
			  AOMDV_Route* route = new AOMDV_Route(nexthop, lasthop);
			  assert(route);
			  LIST_INSERT_HEAD(&reverse_path_list, route, route_link);
			  return route;
        }

链表的遍历：

        inline AOMDV_Route* reverse_path_lookup(nsaddr_t nexthop, nsaddr_t lasthop=0) {
			  AOMDV_Route *route = reverse_path_list.lh_first;

			  // Search the list for a match of id
			  for( ; route; route = route->route_link.le_next) {
					if ( (route->nh_addr == nexthop) && (route->lh_addr == lasthop) )
						return route;     
					}
				return NULL;
				}