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发表于 2012-09-05 09:53 |只看该作者 |倒序浏览

本帖最后由木卫十二于 2012-09-05 09:55 编辑

单链表结构体：

typedef struct node {
char *item;
struct node *next;
} *link;

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在做 free 操作后，依然可以遍历整个链表，只是值全部为零。甚至设置 head = NULL; 也不行。请问这种情况正常吗？
free 操作，对结构体做了哪些改变？

void destroy(link head)
{
printf("destroy(link)\n");
link temp = head;
for(;;)
{
head = temp;
temp = temp->next;
printf("free item => [%s]\n", head->item);
free(head);
head = NULL;
if (temp == NULL)
break;
}
printf("\n");
}

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gdb 下调试，看起来 free 并未改变指针地址，设为 head = NULL 后改变了。但后期 traverse 的时候， head 的地址依然未变。请看下 void destroy(link head) 函数，有什么问题吗？谢谢！

Breakpoint 1, destroy (head=0x804b008) at link.c:60
60 free(head);
(gdb) print head
$1 = (link) 0x804b008
(gdb) n
61 head = NULL;
(gdb) print head
$2 = (link) 0x804b008
(gdb) n
63 if (temp == NULL)
(gdb) print head
$3 = (link) 0x0
(gdb)

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traverse(link)
226 if (head == NULL)
(gdb) print head
$1 = (link) 0x804b008

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另外，下面是我写的单链表操作的实践，能否请看下实现的思路有没有问题？谢谢！

#include <stdio.h>
#include <stdlib.h>
typedef struct node {
char *item;
struct node *next;
} *link;
void destroy(link);
link initialize();
void delete(link, int);
void insert(link, int, char *);
link search(link, char *);
void pop(link);
void push(link, char *);
void traverse(link);
int main()
{
link linkhead = initialize();
pop(linkhead);
push(linkhead, "test1");
push(linkhead, "test2");
push(linkhead, "test3");
push(linkhead, "test4");
push(linkhead, "test5");
push(linkhead, "test2");
push(linkhead, "test7");
pop(linkhead);
push(linkhead, "test3");
delete(linkhead, 3);
traverse(linkhead);
insert(linkhead, 2, "replace 2");
traverse(linkhead);
search(linkhead, "test2");
destroy(linkhead);
traverse(linkhead);
}
void destroy(link head)
{
printf("destroy(link)\n");
link temp = head;
for(;;)
{
head = temp;
temp = temp->next;
printf("free item => [%s]\n", head->item);
free(head);
head = NULL;
if (temp == NULL)
break;
}
printf("\n");
}
link initialize()
{
printf("initialize()\n");
link head = malloc(sizeof(link));
head->item = "I'm the head!";
head->next = NULL;
printf("\n");
return head;
}
void delete(link head, int i)
{
printf("delete(link, int); delete the [%d]'th item.\n", i);
link temp = head;
int j = 0;
for(;;)
{
if (temp->next == NULL)
{
break;
}
if ((i-1) == j)
{
temp->next = temp->next->next;
break;
}
temp = temp->next;
j++;
}
printf("\n");
}
void insert(link head, int i, char *item)
{
printf("insert(link, int, char *); insert item => [%s] as the [%d]'th.\n", item, i);
link temp = head;
link newitem = malloc(sizeof(link));
newitem->item = item;
int j = 0;
for(;;)
{
if (temp->next == NULL)
{
break;
}
if ((i-1) == j)
{
newitem->next = temp->next;
temp->next = newitem;
break;
}
temp = temp->next;
j++;
}
printf("\n");
}
link search(link head, char *item)
{
printf("search(link, item); item => [%s]\n", item);
link temp = head;
int i = 0;
for(;;)
{
if (strcmp(temp->item, item) == 0)
{
printf("found item [%s] at the %d'th item.\n", temp->item, i);
}
if (temp->next == NULL)
{
break;
}
temp = temp->next;
i++;
}
printf("\n");
}
void pop(link head)
{
printf("pop(link)\n");
link temp = head;
for(;;)
{
if (temp->next == NULL)
{
printf("only head item exist. so, don't pop.\n");
break;
}
else if (temp->next->next == NULL)
{
printf("pop item: %s\n", temp->next->item);
temp->next = NULL;
break;
}
temp = temp->next;
}
printf("\n");
}
void push(link head, char *item)
{
printf("push(link, item); item => '%s'\n", item);
link newitem = malloc(sizeof(struct node));
link temp = head;
newitem->item = item;
newitem->next = NULL;
for(;;)
{
if(temp->next == NULL)
{
printf("puch item %s\n", item);
temp->next = newitem;
break;
}
temp = temp->next;
}
printf("\n");
}
void traverse(link head)
{
printf("traverse(link)\n");
if (head == NULL)
{
printf("linkhead is NULL!\n");
exit(0);
}
link temp = head;
for(;;)
{
if(temp->next == NULL)
break;
/* print all, except head. */
temp = temp->next;
printf("get item = %s\n", temp->item);
}
printf("\n");
}