ipc_example.c

// C Program for IPC Message Queue. Adapted from https://www.geeksforgeeks.org/ipc-using-message-queues/

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <cstring>

using namespace std;

// structure for message queue
struct mesg_buffer {
   long mtype;
   char mtext[100];
};

int main(int argc, char** argv)
{
   if (argc < 2)
   {
      cout<<"Need argument to be 'xmt' or 'rcv'"<<endl;
      return 1;
   }
   string xr = argv[1];
  
   // Any int between 0x01 and 0xff:
   int id = 69; 
  
   // Must exist in the filesystem. Not clear what the point is here:
   const char* pathname = "dummy.txt";

   // ftok to generate unique key
   key_t key = ftok(pathname, id);
   if (key < 0)
   {
      printf("Bad key!\n");
      return 1;
   }

   // msgget creates a message queue and returns identifier
   int msgid = msgget(key, 0666 | IPC_CREAT);
   mesg_buffer message;
   if (xr == "xmt")
   {
      // msgsnd to send message and echo to console:
      message.mtype = 1;
      strcpy(message.mtext, "Hello Process!");
      msgsnd(msgid, &message, sizeof(message), 0);
      printf("Data send is : %s \n", message.mtext);
   }
   else
   {
      // msgrcv to receive message then destroy queue:
      msgrcv(msgid, &message, sizeof(message), 1, 0);
      printf("Data Received is : %s \n", message.mtext);
      msgctl(msgid, IPC_RMID, NULL);
   }

   return 0;
}

Example of xmt/rcv interprocess message queuing. Run as two separate instances:

ipc_example rcv &
ipc_example xmt &