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C语言的双链表.html
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C语言的双链表.html
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<!DOCTYPE html>
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<title>C语言的双链表</title>
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<p>
将OSPF PNE代码中的链表的基本操作函数提取出来,并且进行了一些测试的实验。详细的测试文件位于./code/list.c中。下面将各个函数总结如下:
</p>
<h2 id="toc_0.1">链表结构体</h2>
<p>
下面是链表结构体的定义。两个通用的链表结构体LINK和OSPF_GENERIC_NODE是所有链表操控函数的输入参数,其他链表结构体,例如OSPF,都需要强制类型转化为上面两个通用结构体,才能够作为参数传入链表操作函数。
</p>
<pre name="code" class="c">
typedef struct LINK {
struct LINK *sptr_forward_link;
struct LINK *sptr_backward_link;
} LINK;
/* used for pointer manipulation when inserting and removing nodes in a list */
typedef struct OSPF_GENERIC_NODE {
struct OSPF_GENERIC_NODE *sptr_forward_link;
struct OSPF_GENERIC_NODE *sptr_backward_link;
} OSPF_GENERIC_NODE;
typedef struct OSPF {
struct OSPF *sptr_forward_link;
struct OSPF *sptr_backward_link;
int cnt;
} OSPF;
</pre>
<h2 id="toc_0.2">链表操作函数</h2>
<p>
下面是链表通用操作函数。注意,删除链表中的节点函数,形参链表首头位指针的指针,为什么需要这样呢?删除的节点,也许就是链表头所指的节点。也就是说,该形参不仅是输入参数,而且也可能是输出参数(在删除的节点为头节点时)。在测试函数main()中就有这样的一个实例,需要特别注意。
</p>
<pre name="code" class="c">
/*************************************************************************/
void ospf_add_entry_to_list(LINK * sptr_link, LINK * sptr_link_to_add)
{
if (sptr_link == NULL) {
return;
}
if (sptr_link_to_add == NULL) {
return;
}
sptr_link_to_add->sptr_backward_link = sptr_link->sptr_backward_link;
if (sptr_link->sptr_backward_link != NULL) {
sptr_link->sptr_backward_link->sptr_forward_link =
sptr_link_to_add;
} else {
sptr_link->sptr_forward_link = sptr_link_to_add;
}
sptr_link->sptr_backward_link = sptr_link_to_add;
sptr_link_to_add->sptr_forward_link = NULL;
}
/************************************************************************/
void ospf_delete_entry_from_list
(
LINK *sptr_list_link,
LINK *sptr_link_to_delete
)
{
if (sptr_list_link == NULL)
{
return;
}
if (sptr_link_to_delete == NULL)
{
return;
}
if ((sptr_link_to_delete->sptr_forward_link == NULL) &&
(sptr_link_to_delete->sptr_backward_link == NULL)) /* 1 entry in list */
{
sptr_list_link->sptr_forward_link = NULL;
sptr_list_link->sptr_backward_link = NULL;
return;
}
if (sptr_link_to_delete->sptr_backward_link == NULL)
{
/* first entry in list */
sptr_list_link->sptr_forward_link =
sptr_link_to_delete->sptr_forward_link;
}
else
{
sptr_link_to_delete->sptr_backward_link->sptr_forward_link =
sptr_link_to_delete->sptr_forward_link;
}
if (sptr_link_to_delete->sptr_forward_link == NULL) /* last entry in list */
{
sptr_list_link->sptr_backward_link =
sptr_link_to_delete->sptr_backward_link;
}
else
{
sptr_link_to_delete->sptr_forward_link->sptr_backward_link =
sptr_link_to_delete->sptr_backward_link;
}
sptr_link_to_delete->sptr_forward_link = NULL;
sptr_link_to_delete->sptr_backward_link = NULL;
}
/******************************************************************************/
void ospf_insert_node_in_list(OSPF_GENERIC_NODE * sptr_node,
OSPF_GENERIC_NODE * sptr_previous_node)
{
sptr_node->sptr_backward_link = sptr_previous_node;
sptr_node->sptr_forward_link = NULL; /* always added at end */
sptr_previous_node->sptr_forward_link = sptr_node;
return;
}
/******************************************************************************/
void ospf_add_node_to_end_of_list(OSPF_GENERIC_NODE * sptr_node,
OSPF_GENERIC_NODE *
sptr_first_node_in_list)
{
if (sptr_first_node_in_list->sptr_forward_link == NULL) {
sptr_first_node_in_list->sptr_forward_link = sptr_node;
sptr_first_node_in_list->sptr_backward_link = sptr_node;
sptr_node->sptr_backward_link = sptr_first_node_in_list;
sptr_node->sptr_forward_link = NULL;
return;
}
ospf_add_entry_to_list((LINK *) sptr_first_node_in_list,
(LINK *) sptr_node);
return;
}
/******************************************************************************/
void ospf_remove_node_from_list(OSPF_GENERIC_NODE ** ptr_sptr_first_node, OSPF_GENERIC_NODE * sptr_node)
{
OSPF_GENERIC_NODE *sptr_previous_node;
OSPF_GENERIC_NODE *sptr_next_node;
sptr_previous_node = NULL;
sptr_next_node = NULL;
if ((*ptr_sptr_first_node == NULL) || (sptr_node == NULL))
return;
if (*ptr_sptr_first_node == sptr_node)
{
if (sptr_node->sptr_forward_link != NULL)
{
*ptr_sptr_first_node = sptr_node->sptr_forward_link;
/* Mistral Added on July 25th */
if(*ptr_sptr_first_node)
{
(*ptr_sptr_first_node)->sptr_backward_link =
sptr_node->sptr_backward_link;
}
}
else
{
*ptr_sptr_first_node = NULL;
}
sptr_node->sptr_forward_link = NULL;
sptr_node->sptr_backward_link = NULL;
return;
}
if ( *ptr_sptr_first_node != NULL )
{
ospf_delete_entry_from_list
((LINK *) *ptr_sptr_first_node, (LINK *) sptr_node);
}
return;
}
/******************************************************************************/
OSPF_GENERIC_NODE *ospf_free_entire_list(OSPF_GENERIC_NODE * sptr_first_node_in_list)
{
OSPF_GENERIC_NODE *sptr_node;
OSPF_GENERIC_NODE *sptr_next_node;
for (sptr_node = sptr_first_node_in_list; sptr_node != NULL;
sptr_node = sptr_next_node) {
sptr_next_node = sptr_node->sptr_forward_link;
ospf_remove_node_from_list((OSPF_GENERIC_NODE **) &sptr_first_node_in_list, sptr_node);
free((void *) sptr_node);
sptr_node = NULL;
}
return (NULL);
}
</pre>
<h2 id="toc_0.3">链表测试用例</h2>
<p>
下面为测试函数,用于测试上面的链表操作函数。有一个地方没有明白,销毁整个链表时,使用的是free((void *) sptr_node),指针的类型都改变了,free函数还知道我真正的链表结构体(本例中的OSPF结构体)大小吗?
</p>
<pre name="code" class="c">
void printList(OSPF* ptr)
{
OSPF* ptr_node;
printf("the list node: ");
for(ptr_node = ptr;ptr_node != NULL; ptr_node = ptr_node->sptr_forward_link)
{
printf("%d->",ptr_node->cnt);
}
printf("NULL\n");
return;
}
int main(int argc,char** argv)
{
OSPF* ptr = NULL;
OSPF* ptr_node = NULL;
OSPF* ptr_node_del = NULL;
/* init the list */
if(NULL == (ptr_node = malloc(sizeof(OSPF))))
{
printf("malloc memory failed\n");
return 0;
}
ptr_node->cnt = 0;
ptr = ptr_node;
printList(ptr);
/* add test */
if(NULL == (ptr_node = ptr_node_del = malloc(sizeof(OSPF))))
{
printf("malloc memory failed\n");
return 0;
}
ptr_node->cnt = 1;
ospf_add_node_to_end_of_list((OSPF_GENERIC_NODE *)ptr_node,(OSPF_GENERIC_NODE *)ptr);
printList(ptr);
/* add another */
if(NULL == (ptr_node = malloc(sizeof(OSPF))))
{
printf("malloc memory failed\n");
return 0;
}
ptr_node->cnt = 2;
ospf_add_node_to_end_of_list((OSPF_GENERIC_NODE *)ptr_node,(OSPF_GENERIC_NODE *)ptr);
printList(ptr);
/* delete test */
ospf_remove_node_from_list((OSPF_GENERIC_NODE **)& ptr,(OSPF_GENERIC_NODE *)ptr_node_del);
free(ptr_node_del);
ptr_node_del = NULL;
printList(ptr);
/* delete the first node test */
/* the first node of the list is deleted,ptr is pointed to another head address of the list.
* at this moment,we lost the address of the first node we deleted,so how to free this node ? */
/*
ospf_remove_node_from_list((OSPF_GENERIC_NODE **)& ptr,(OSPF_GENERIC_NODE *)ptr);
*/
/* just the resean above,we should rewrite the code as below */
ptr_node_del = ptr;
ospf_remove_node_from_list((OSPF_GENERIC_NODE **)& ptr,(OSPF_GENERIC_NODE *)ptr_node_del);
free(ptr_node_del);
ptr_node_del = NULL;
printList(ptr);
/* free the all list */
ospf_free_entire_list((OSPF_GENERIC_NODE *)ptr);
ptr = NULL;
printList(ptr);
return 0;
}
</pre>
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