Thread: How do I pass an array of structures to the *nix read() function.

I'm trying to pass an array of structures to the *nix read() function. Here is the code...

Code:

#include <stdio.h>
#include <stdlib.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>


struct bbs {
  char *s;
  int i;
};

struct bbs user[1];

int main(void)
{

  user[0].s = "chad\n";
  user[0].i = 1;

  /*user[1].s = "was\n";
  user[1].i = 1;

  user[2].s = "here\n";
  user[2].i = 1;
  */


  ssize_t n;
  int fd;

  if ((fd = open("/home/cdalten/oakland/ho", O_RDWR)) < 0) {
    perror("Can't open file\n");
    exit(EXIT_FAILURE);
  }

  write(fd, &user, sizeof(struct bbs));

  while((n = read(fd, &user, sizeof(struct bbs))) > 0 ) {
    printf("The string is: %s\n", user[1].s);
  }

  close(fd);
 
  exit(EXIT_SUCCESS);
}

And here is what I get when I compile and run the code.

[cdalten@localhost oakland]$ gcc -g -Wall wr.c -o wr
[cdalten@localhost oakland]$ ./wr
The string is: (null)
The string is: (null)
[cdalten@localhost oakland]$

1) You haven't allocated any memory to the bbs objects.
2) Even if you had, you would need to pass the address of the memory (not the structure) to the read routine (otherwise, you'd just be overwriting the pointer).
3) When you do finally allocate some memory, just remember to pass the size of the buffer (not the structure) as the third parameter of the read function.