链式队列的实现

typedef struct node{

        int data;

        struct node *next;

}linklist;

 

typedef struct{

        linklist *front;

        linklist *rear;

}linkqueue;

 

void setnull(linkqueue *p){           //建立空队

        linklist *p,*r;

        p=q->front;

        while(p){

                r=p;

                p=p->next;

                free(r);

          }

         q->front=q->rear=(linklist *)malloc(sizeof(linklist));

         q->front->next=NULL;

         return;

}

 

int empty_queue(linkqueue *q){        //置空队

         return (q->front==q->rear);

}

 

void en_queue(linkqueue *q,int value){          //入队

         q->rear->next=(linklist *)malloc(sizeof(linklist));

         q->rear=q->rear->next;

         q->rear->data=value;

         q->rear->next=NULL;

         return;

}

 

int de_queue(linkqueue *q,int *x){        //出队

         linklist *r;

         if(empty_queue(q)){

                  printf("link queue is empty!/n");

                  return -1;

         }

         r=q->front;

         q->front=r->next;

         free(r);

         *x=q->front->data;

         return 0;

}

 

void visit_queue(linkqueue *q){                //遍历队

        linklist *p;

        printf("queue:");

        p=q->front->next;

        while(p){

                 printf("%d",p->data);

                 p=p->next;

        }

        printf("/n");

        return;

}

 

 

第二种定义：

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <assert.h>
#include <stdlib.h>
#include <stdbool.h>
#include <errno.h>

#include "myhead.h"

void perror_exit(const char *info)
{
 perror(info);
 exit(-1);
}

/* set a empty queue, front and rear
pointer both point to a head node*/
void queue_init(linkqueue *pq)
{
 *pq = (linkqueue)malloc(sizeof(linknode) * 2);
 (*pq)->front = (*pq)->rear = (linklist)malloc(sizeof(linknode));
 (*pq)->rear->next = NULL;
}

/* check the queue is empty or not */
bool isempty(linkqueue q)
{
 assert(q);
 if(q->front == q->rear)
  return true;
 return false;
}

/* delete elements from the queue */
bool out_queue(linkqueue q, int *element)
{
 assert(q);
 if(isempty(q)){
  fprintf(stderr, "the queue is empty./n");
  return false;
 }

 linklist p = q->front;

 q->front = q->front->next;
 free(p);
 *element = q->front->data;

 return true;
}

/* add element into the queue */
bool en_queue(linkqueue q, int element)
{
 assert(q);
 linklist pnew;
 pnew = (linklist)malloc(sizeof(linknode));
 if(pnew == NULL){
  perror("malloc failed");
  return false;
 }
 pnew->data = element;
 pnew->next = NULL;

 q->rear->next = pnew;
 q->rear = pnew;

 return true;
}

/* show all elements in the current queue */
void show(linkqueue q)
{
 assert(q);
 if(isempty(q)){
  fprintf(stderr, "the queue is empty./n");
  return;
 }

 linklist p;
 p = q->front->next;

 int i = 1;
 do{
  fprintf(stderr, "[%d]: %d/n", i++, p->data);
  p = p->next;
 }while(p != NULL);

 return;
}

/* thread handler function */
/*void *tfn(void *arg)
{
 assert(arg);
 linkqueue q = (linkqueue)arg;
 int element;

 while(1){
  sleep(5);
  if(out_queue(q, &element)){
   fprintf(stderr, "%d has been deleted"
     " from the queue/n", element);
   show(q);
  }
 }
}
*/

/* safely scanf */
bool s_scanf(const char *format, int *ele_loc)
{
 int ret1, ret2;
 while((ret1=scanf(format, ele_loc)) != 1 || /
  (ret2=getchar()) != '/n'){

  if((ret1 != 1) && (errno == EINTR))
   continue;

  while(getchar() != '/n'); // discards invalid inputs

  fprintf(stderr, "input invalid!/n");
  //fprintf(stderr, "pls insert an integer: ");
 }
 return true;
}