C++ - msgsnd & msgrcv communication between 2 different programs - c++

Question

I have two programs and I want them to communicate together by msgrcv() && msgsnd(). I so have a master program which init the message queue and start the 2 others programs:
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string>
#include <iostream>
#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>
int main() {
int qid = msgget(ftok(".",'u'), 0);
char* params[3];
params[1] = (char *)malloc(sizeof(char) * 9);
sprintf(params[1], "%d", qid);
params[2] = NULL;
printf("qid = %d and qid(str) = %s", qid, params[1]);
// return (0);
//spawning two child processes
pid_t cpid = fork();
if (cpid == 0) {
params[0] = (char*)"./sender";
execv(params[0], params);
exit(0);
}
cpid = fork();
if (cpid == 0) {
params[0] = (char*)"./receiver";
execv(params[0], params);
exit(0);
}
while (wait(NULL) != -1); // waiting for both children to terminate
msgctl(qid, IPC_RMID, NULL);
std::cout << "parent proc: " << getpid()
<< " now exits" << std::endl;
exit(0);
}
I also prepare the parameters and start the both following programs:
sender
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <iostream>
#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>
int main(int ac, char **av) {
if (ac != 2)
return (-1);
// create my msgQ with key value from ftok()
// int qid = msgget(IPC_PRIVATE, IPC_EXCL|IPC_CREAT|0600);
int qid = atoi(av[1]);
// declare my message buffer
struct buf {
long mtype; // required
char greeting[50]; // mesg content
};
buf msg;
int size = sizeof(msg)-sizeof(long);
std::cout << "Welcome in the prog assignment 2! Type [exit] to stop the program." << std::endl;
bool exit = false;
while (!exit)
{
std::cout << getpid() << ": ";
std::cin.getline(msg.greeting, 50, '\n');
std::cout << msg.greeting << std::endl;
msg.mtype = 114; // only reading mesg with type mtype = 114
if (strcmp(msg.greeting, "exit") == 0)
exit = true;
msgsnd(qid, (struct msgbuf *)&msg, size, 0);
}
}
receiver
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <iostream>
#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>
int main(int ac, char **av) {
int i = 0;
while (i < ac)
printf("AV: %s\n", av[i++]);
if (ac != 2)
return (-1);
// int qid = msgget(IPC_PRIVATE, IPC_EXCL|IPC_CREAT|0600);
int qid = atoi(av[1]);
// declare my message buffer
struct buf {
long mtype;
char greeting[50];
};
buf msg;
int size = sizeof(msg)-sizeof(long);
bool exit = false;
while (!exit)
{
msgrcv(qid, (struct msgbuf *)&msg, size, 114, 0);
if (strcmp(msg.greeting, "exit") == 0)
exit = true;
std::cout << getpid() << msg.greeting << std::endl;
}
std::cout << "get out" << std::endl;
}
It doesn't work and I'm not sure to understand why because, I'm creating the message queue, passing it as parameter, then I put it back as int and then use it. However, it just gives me an infinite loop of weird display, why?
ANy help is welcome.. Thank !