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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naourez <naourez_m@yahoo.fr> wrote:
> hi everybody

Please don't post the same stuff again and again. This isn't IRC and
it can take more than a day that your question gets seen by all people.

> i ve a pb with this code

<snipped irrelevant code>

>       char *data,*message;
>       int mode,*flag,c;

>       printf("entrez ici votre message \n");
>       fflush(stdin);
>       fgets(message,sizeof(message),stdin);

'message' is still an unnitialized pointer, pointing to some random
location. When fgets() now tries to use the pointer it crahes You
need to make 'message' point to some memory you own, either an
array of chars, a malloc()ed memory area or to the shared memory
segment you just got. Moreover, "sizeof(message)" is the size of a
char pointer and that's rather unlikely to be the size of the buffer
you want pass to fgets().
Regards, Jens
--
\   Jens Thoms Toerring  ___  Jens.Toerring@physik.fu-berlin.de
\__________________________  http://www.toerring.de

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