使用bsd的queue.h实现简单队列

队列是c中经常需要使用的数据结构，写一个0bug的队列header对于将来的代码复用很有用。

我选择使用bsd实现的队列结构，一是因为它实现简单，一个头文件里全是宏定义，二是因为它是BSD协议，代码可以随便用。

在linux下，在<sys/queue.h>里定义了五个数据结构，分别是simple linked list, list, simple queue, tail queue和circuled queue

这里介绍使用simple queue，因为simple可以支持在队头队尾分别进行插入和删除，足够简单,基本足够我日常使用。（我基本上用无优先级的队列）

下面这段代码定义task_t的队列，分别赋值0, 1, 2, 3, 4。然后删除3，最后循环打印这个队列

#include <stdio.h>                                                                #include <stdlib.h>                                                               #include <sys/queue.h>                                                                                                                                              struct task_t {                                                                       int data;                                                                         SIMPLEQ_ENTRY(task_t) entries;                                                };                                                                                                                                                                     // declare type                                                                      SIMPLEQ_HEAD(taskqueue_t, task_t);                                                   // define variant                                                                                                                                       struct taskqueue_t task_head;                                                                                                                                             int main(int argc, const char *argv[])                                               {                                                                                        struct task_t t[5];                                                                  int i;                                                                                                                                                                    SIMPLEQ_INIT(&task_head);                                                            for (i = 0; i < 5; i++)                                                              {                                                                                        memset(&t[i], 0, sizeof(t[i]));                                                      t[i].data = i;                                                                       SIMPLEQ_INSERT_TAIL(&task_head, &t[i], entries);                                 }                                                                                 // delete one element in the queue                                                SIMPLEQ_REMOVE(&task_head, &t[3], task_t, entries);                               /*if ((item->list.sqe_next = item->list.sqe_next->list.sqe_next)      == NULL) {     (&dealqueue)->sqh_last = &(item)->list.sqe_next;    }直接使用其中的删除语句，程序崩溃*/                                                                                  struct task_t *item;                                                              SIMPLEQ_FOREACH(item, &task_head, entries) {                                          printf("data: %i\n", item->data);                                             }                                                                                    return 0;                                                                        }

• 我不喜欢把变量声明和定义写一起，分开比较好。
• queue.h里面大多是使用指针的宏，所以在写宏的时候注意传指针就不容易错。
• SIMPLEQ_ENTRY(task_t)定义了每个元素与其它前后元素相联系的结构体，可以通过它找到前后元素，至于这个结构体叫什么名字，都无所谓。（所以是否可以把这个结构体写进宏里更能精简代码呢？我觉得完全是可以的）
• 如果queue.h可以有pop的宏就好了，查询节点再删除这样的操作显得很麻烦