hi everybody
i ve a pb with this code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#define SHM_SIZE 4096  /* make it a 4K shared memory segment */

int main()
{
key_t key,key_flag;
int shmid,id_flag;
char *data,*message;
int mode,*flag,c;


/* make the key: */
if ((key_flag = ftok("shm.c", 'A')) == -1) {
perror("ftok");
exit(1);
}
if ((id_flag= shmget(key_flag,sizeof(int), 0644 | IPC_CREAT)) == -1) {
perror("shmget");
exit(1);
}
flag =(int*) shmat(id_flag, NULL, 0);
if (flag ==(int*) -1) {
perror("shmat");
exit(1);
}
printf("quel est votre choix \n");
scanf("%d",&c);
(*flag)=c;
printf("le drapeau ecrit dans le segment a pour numero: \"%d\"\n",c);


switch(c)
{
case 1:
printf("demande d'établissement d'une connexion\n");
break;
case 2:
printf("demande d'ouverture de session\n");
break;
case 3:
printf("demande d'envoi de message  \n");

{if ((key = ftok("shm.c", 'R')) == -1) {
perror("ftok");
exit(1);
}

/* connect to (and possibly create) the segment: */
if ((shmid = shmget(key,SHM_SIZE, 0644 | IPC_CREAT)) == -1) {
perror("shmget");
exit(1);
}

/* attach to the segment to get a pointer to it: */
data =(char*) shmat(shmid, NULL, 0);
if (data == (char*)-1) {
perror("shmat");
exit(1);
}

/* modify the segment */

printf("entrez ici votre message \n");
fflush(stdin);
fgets(message,sizeof(message),stdin);
printf("message ecrit dans le segment: \"%s\"\n",message);
strncpy(data, message,SHM_SIZE);


/* detach from the segment: */
if (shmdt((char*)data) == -1) {
perror("shmdt1");
exit(1);
}

break;
}
default:
break;
}
if (shmdt(flag) == -1) {
perror("shmdt2");
exit(1);
}

return 0;
}
in fact where c ==3
i obtain segmentation fault before i even enter the message
and i don't see why
any ideas !!
thanks a lot

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