消息队列的创建，删除，发送，读取（含概念）

 消息队列

 1.特点

 2.相关函数

 ps:

 消息队列实现单个进程的发送和读取

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <stdlib.h>
#include <string.h>

struct msgbuf
{
   long mtype;//消息类型
   char mtest[128];//消息内容容器
   char ID[4];	
};


int main()
{
  struct msgbuf sendbuf,readbuf;
  int msgid;//消息队列id
  int readret;//读取到的字节数
  msgid = msgget(IPC_PRIVATE,0755);
  if(msgid == -1)
  {
      printf("create message queue failed !\n");
      return -1;

  }
 
  printf("create message queue sucess ,msgid = %d\n",msgid);
  system("ipcs -q");//终端打印出消息队列详细信息
  

  //init msgbuf

  sendbuf.mtype = 100;
  printf("please input to message queue :\n");
  fgets(sendbuf.mtest,128,stdin);//手动键盘输入内容

  //send message to message queue
  msgsnd(msgid,(void *)&sendbuf,strlen(sendbuf.mtest),0);

  //read
  memset(readbuf.mtest,0,128);//把readbuf中内容全部清零
  readret = msgrcv(msgid,(void *)&readbuf,128,100,0);//读取
  printf("message is %s\n",readbuf.mtest);
  printf("total have %d byte\n",readret);

  
  return 0;
}

运行结果：创建了id为524290的消息队列，键盘输入ni到该队列中，读取到内容为ni，并且为3个字节（还包含结束符‘\0’）。

我们再运行一次，发现524290消息队列中字节数为0，明明刚刚我们写入了内容，为什么此时为0呢？？？

原因：消息队列的性质就是如此，当从其中读取完数据后，他就会把该节点中的内容全部清除，但是该节点仍然存在鱼内核中。

ftok函数介绍

消息队列实现多个进程间的数据发送和读取

两个进程代码如下：

/*************msg_write.c*************/
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <stdlib.h>
#include <string.h>

struct msgbuf
{
   long mtype;
   char mtest[128];
   char ID[4];	
};


int main()
{
  struct msgbuf sendbuf;
  int msgid;
  
  key_t key;
  key = ftok("a.c",1);
  msgid = msgget(key,IPC_CREAT|0755);
  if(msgid == -1)
  {
      printf("create message queue failed !\n");
      return -1;

  }
 
  printf("create message queue sucess ,msgid = %d\n",msgid);
  system("ipcs -q");
  

  //init msgbuf

  sendbuf.mtype = 100;
  while(1)
  {
    memset(sendbuf.mtest,0,128);
    printf("please input to message queue :\n");
    fgets(sendbuf.mtest,128,stdin);
    msgsnd(msgid,(void *)&sendbuf,strlen(sendbuf.mtest),0); //send message to message queue
  }

  return 0;
}











/**************msg_read.c***********/
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <stdlib.h>
#include <string.h>

struct msgbuf
{
   long mtype;
   char mtest[128];
   char ID[4];	
};


int main()
{
  struct msgbuf readbuf;
  int msgid;
  key_t key;
  int readret;
  key = ftok("a.c",1);
  msgid = msgget(key,IPC_CREAT|0755);
  if(msgid == -1)
  {
      printf("create message queue failed !\n");
      return -1;

  }
 
  printf("create message queue sucess ,msgid = %d\n",msgid);
  system("ipcs -q");
  

  //init msgbuf

  readbuf.mtype = 100;


  while(1) //read
  { 
    memset(readbuf.mtest,0,128);//把readbuf中内容全部清零
    readret = msgrcv(msgid,(void *)&readbuf,128,100,0);
    printf("message is %s\n",readbuf.mtest);
    printf("total have %d byte\n",readret);
  }
  
  return 0;
}

 编译：gcc msg_write.c -o msg_write

      gcc msg_read.c -o msg_read

打开两个终端，分别运行 ./msg_write  和   ./msg_read

运行结果如下：