/*
 * msgQ1.c++ POSIX message queue
 * $ g++ -Wall msgQ1.c++ -lrt
 * $ sudo ./a.out w; ./a.out r
 */
#include <iostream>
using namespace std;
#include <fcntl.h>           
#include <sys/stat.h>        
#include <mqueue.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>

#define MSGSIZE 1024
#define MAXMSG  16

int main(int ac, char *av[]){
    struct mq_attr attr;
    int err, msgLen;
    mqd_t mqd;

    if(ac < 2){
      cerr << "r/w not specified\n";
      exit(1);
    }    
    attr.mq_maxmsg = MAXMSG;
    attr.mq_msgsize = MSGSIZE;
    attr.mq_flags = 0;
    attr.mq_curmsgs = 0; 

    if(av[1][0] == 'w'){
       char buff[MSGSIZE]; 
       int prio=0;

       mqd = mq_open("/myMq", O_WRONLY | O_CREAT, 0777, &attr);
       if(mqd == -1){
         cerr << "mq_open() problem: " << errno << endl;
         exit(1);
       }
       cout << "Enter message (terminate with Ctrl-D): ";
       while(1) {
          cin.getline(buff, MSGSIZE);
          err = mq_send(mqd, buff, strlen(buff), prio++);
          if(err == -1){
            cerr << "mq_send() fails\n";
            exit(1);
          }
          if(cin.eof()) break;
       }
    } 
    if(av[1][0] == 'r'){
       char buff[MSGSIZE]; 
       mqd = mq_open("/myMq", O_RDONLY | O_CREAT, 0777, &attr);
       if(mqd == -1){
         cerr << "mq_open() problem: " << errno << endl;
         exit(1);
       }
       cout << "Reader reads message: \n";
       while((msgLen = mq_receive(mqd, buff, MSGSIZE, NULL)) != -1){
         buff[msgLen]='\0';
         if(msgLen != 0)
           cout << "Received message: " << buff << endl; 
       }
    }
    mq_close(mqd);
    return 0;
}