Problems on shmem access

Hi there again!

It's me again and my newbie problems :P

I've been trying to read a string from a shared memory block but with no success.
I can read it OK if I use static name[] and content[] but I can't get anything using pointers.

I'm tired of playing around to get a solution. I give you some short versions. I run one.c then two.c

I'm sure it must be a newbie bug :S

onetwo.h

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/shm.h>

#define BUFFER_SLOTS		10
#define KEY             1919

typedef struct message {
   int to, from, type;
   char *name;
   char *content;
} message;

typedef struct buffer {
   int pos;
   message msg[BUFFER_SLOTS];
} buffer;

one.c

Code:

#include "onetwo.h"

int main() {
   buffer *BUF;
   int bufshmid;
   
   bufshmid = shmget(KEY, sizeof(struct buffer), 0666 | IPC_CREAT);
   
   if ((BUF = shmat(bufshmid, NULL, 0)) == (buffer *)-1) {
      printf("!!! could not attach to shared memory");
      exit(1);
   }
   
   message *msg;
   msg = malloc(sizeof(struct message));
   msg->to = 1;
   msg->from = 2;
   msg->type = 3;
   msg->name = malloc(strlen("hello")+1);
   msg->content = malloc(strlen("world")+1);
   strcpy(msg->name, "hello");
   strcpy(msg->content, "world");
   
   memcpy(&BUF->msg[0], msg, sizeof(struct message));
   printf("all done\n");
   sleep(5);
   return 0;
}

two.c

Code:

#include "onetwo.h"

int main() {
   buffer *BUF;
   int bufshmid;
   
   bufshmid = shmget(KEY, sizeof(struct buffer), 0666 | IPC_CREAT);
   
   if ((BUF = shmat(bufshmid, NULL, 0)) == (buffer *)-1) {
      printf("!!! could not attach to shared memory");
      exit(1);
   }
   
   printf("type: %i\n", BUF->msg[0].type);
   printf("name: %s\n", BUF->msg[0].name);
   
   printf("all done\n");
   return 0;
}

I suppose you want to read memory from two.c. First thing I noticed is the line

Code:

bufshmid = shmget(KEY, sizeof(struct buffer), 0666 | IPC_CREAT);

It creates the segment. For reading you should place instead

Code:

bufshmid = shmget(KEY, 0, 0);