Example child is based on

/* #include <cstdlib> */
#include <iostream>
#include <cerrno>
#include <limits>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

#define BUFSIZ  512

struct my_msg_st {
   long int my_msg_type;
   char some_text[BUFSIZ];
};


int main(int argc, char** argv)
{

  int running = 1;
  int msgid;
  struct  my_msg_st some_data;
  long int msg_to_receive = 1;

  /* Set up the message queue */
  msgid = msgget((key_t) 1234, 0666 | IPC_CREAT);

  if (msgid == -1) {
     cout << "msgget failed" << endl;
     exit(EXIT_FAILURE);
  }

  /* Retrieve messages from the queue until an "end" is encountered. */
  while (running) {
    if (msgrcv(msgid, (void *)&some_data, BUFSIZ,
               msg_to_receive, 0) == -1) {
       cout << "msgrev failed" << endl;
       exit(EXIT_FAILURE);
    }

    cout << "You wrote: " << some_data.some_text << endl;

    if (strncmp(some_data.some_text, "end", 3) == 0) {
       running = 0;
    }
    sleep(1);
  }

  if (msgctl(msgid, IPC_RMID, 0) == -1) {
    cout << "msgctl(IPC_RMID) failed" << endl;
    exit(EXIT_FAILURE);
  }

  exit(EXIT_SUCCESS);
}