牵着老婆满街逛

严以律己,宽以待人. 三思而后行.
GMail/GTalk: yanglinbo#google.com;
MSN/Email: tx7do#yahoo.com.cn;
QQ: 3 0 3 3 9 6 9 2 0 .

TAILQ Example

from:http://unx.ca/log/2006/08/19/tailq-example/

I plan to use this blog to post codebits that I find myself sending to people over and over again. The first example is how to use a TAILQ from sys/queue.h found on the BSDs. Many Linux distributions also have sys/queue.h but may be missing certain macros such as TAILQ_FOREACH(). At the very least I hope this enticies some newer C programmer to use queue.h rather than rolling their own linked list. I’ll jump directly to the code as I feel it is more or less self explanatory.

The following code can be downloaded here.

/*
 * TAILQ example program.
 */
#include <stdlib.h>
#include <stdio.h>
/*
 * On many OpenBSD/NetBSD/FreeBSD you could include <sys/queue.h>, but
 * for portability we’ll include the local copy.
 */
#include "queue.h"
/*
 * This structure defines each item in our tail queue.  It must also
 * contain an item (TAILQ_ENTRY) that points to the next and previous
 * items in the tail queue.
 *
 * For simplicity, we will be creating a list of integers.
 */
struct tailq_entry {
int value;
/*
         * This holds the pointers to the next and previous entries in
         * the tail queue.
         */
TAILQ_ENTRY(tailq_entry) entries;
};
/*
 * Our tail queue requires a head, this is defined using the
 * TAILQ_HEAD macro.
 */
TAILQ_HEAD(, tailq_entry) my_tailq_head;
int
main(int argc, char **argv)
{
/* Define a pointer to an item in the tail queue. */
struct tailq_entry *item;
/* In some cases we have to track a temporary item. */
struct tailq_entry *tmp_item;
int i;
/* Initialize the tail queue. */
TAILQ_INIT(&my_tailq_head);
/* Add 10 items to the tailq queue. */
for (i = 0; i < 10; i++) {
/*
                 * Each item we want to add to the tail queue must be
                 * allocated.
                 */
item = malloc(sizeof(*item));
if (item == NULL) {
perror("malloc failed");
exit(EXIT_FAILURE);
}
/* Set the value. */
item->value = i;
/*
                 * Add our item to the end of tail queue. The first
                 * argument is a pointer to the head of our tail
                 * queue, the second is the item we want to add, and
                 * the third argument is the name of the struct
                 * variable that points to the next and previous items
                 * in the tail queue.
                 */
TAILQ_INSERT_TAIL(&my_tailq_head, item, entries);
}
/* Traverse the tail queue forward. */
printf("Forward traversal: ");
TAILQ_FOREACH(item, &my_tailq_head, entries) {
printf("%d ", item->value);
}
printf("n");
/* Insert a new item after the item with value 5. */
printf("Adding new item after 5: ");
TAILQ_FOREACH(item, &my_tailq_head, entries) {
if (item->value == 5) {
struct tailq_entry *new_item =
malloc(sizeof(*new_item));
if (new_item == NULL) {
perror("malloc failed");
exit(EXIT_FAILURE);
}
new_item->value = 10;
TAILQ_INSERT_AFTER(&my_tailq_head, item, new_item,
entries);
break;
}
}
/* Do another forward traversal to show the newly added item. */
TAILQ_FOREACH(item, &my_tailq_head, entries) {
printf("%d ", item->value);
}
printf("n");
/*
         * Delete the item with the value 3.
         *
         * We can’t use TAILQ_FOREACH here as TAILQ_FOREACH is not
         * safe against deletions during the traversal.  Some variants
         * of queue.h have TAILQ_FOREACH_MUTABLE or TAILQ_FOREACH_SAFE
         * which are safe against deletions.
         */
printf("Deleting item with value 3: ");
for (item = TAILQ_FIRST(&my_tailq_head); item != NULL; item = tmp_item)
{
tmp_item = TAILQ_NEXT(item, entries);
if (item->value == 3) {
/* Remove the item from the tail queue. */
TAILQ_REMOVE(&my_tailq_head, item, entries);
/* Free the item as we don’t need it anymore. */
free(item);
break;
}
}
/* Another forward traversal to show that the value 3 is now gone. */
TAILQ_FOREACH(item, &my_tailq_head, entries) {
printf("%d ", item->value);
}
printf("n");
/* Free the entire tail queue. */
while (item = TAILQ_FIRST(&my_tailq_head)) {
TAILQ_REMOVE(&my_tailq_head, item, entries);
free(item);
}
/* The tail queue should now be empty. */
if (!TAILQ_EMPTY(&my_tailq_head))
printf("tail queue is NOT empty!n");
return 0;
}

posted on 2007-08-21 01:45 杨粼波 阅读(1057) 评论(0)  编辑 收藏 引用


只有注册用户登录后才能发表评论。
【推荐】超50万行VC++源码: 大型组态工控、电力仿真CAD与GIS源码库
网站导航: 博客园   IT新闻   BlogJava   知识库   博问   管理