Usage of message queue fork + execlp + ftok - c

Question

The main purpose here is to create a message queue by executing thise command : ./create_msg_queue fileForQueue
We want to create the file fileForQueue if it doesn't exist.
Regarding my code, if the file doesn't exist, I get this error
ftok: No such file or directory
So how can I have this file create BEFORE ftok() is called with the file name ?
Provided code :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
// IPC and KEYS -------------
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/wait.h>
//---------------------------
#define _XOPEN_SOURCE
// message structure
typedef struct {
// id message
long type;
// Size : 12 bytes
double mesure;
pid_t pidClient;
} message_t;
int main (int argc, char * argv []) {
key_t key;
message_t message;
int file;
int pid;
// Check arg number
if (argc != 2) {
fprintf(stderr, "Syntaxe : %s fichier_clé\n",argv[0]);
exit(EXIT_FAILURE);
}
// Create the empty file given in parameter
if ((pid = vfork()) == -1)
{
perror("fork");
exit(1);
}
if (pid)
{
// code replacement to create the FILE
execlp("touch", "touch", argv[1], NULL);
perror("execlp");
exit(1);
}else
{
// Trying to wait for the forked() process to finish its file creation
wait (NULL);
// I GET ERROR HERE IF THE FILE DON'T EXIST BEFORE I LAUNCH THE PROGRAM
// Create key with the file given in parameter and then created
if ((key = ftok(argv[1], 0)) == -1) {
// errNo value
perror("ftok");
exit(EXIT_FAILURE);
}
// Create message queue
if ((file = msgget(key, IPC_CREAT | 0666)) == -1) {
perror("msgget");
exit(EXIT_FAILURE);
}
// Registering message content
message.type = 1;
message.mesure = -1;
message.pidClient = getpid();
// Sending message
if (msgsnd(file, (void *) & message, 12, 0) <0) {
perror("msgsnd");
exit(EXIT_FAILURE);
}
}
return EXIT_SUCCESS;
}
Thanks in advance for help. I struggle :)

Answer 1

key_t ftok(const char *path, int id);
ftok(argv[1], 0))
Only the low-order 8-bits of id are significant. The behavior of
ftok() is unspecified if these bits are 0.
Also note that you have to
#define _XOPEN_SOURCE
at the very begin