Thread: Pointer problem

Hi I am new in C programming and I am facing a problem with the pointer in this program that takes a file path and returns stats about the file by using the stat system call :

Code:

#include <sys/types.h>
#include <sys/stat.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>

void serious_error(char *msg) {
  perror(msg);
  exit(EXIT_FAILURE);
}

/* Fonction principale  */

int main(int argc, char **argv) {
  struct stat status, *buffer;
  int r;

  r = stat(argv[1], buffer);
  if (r < 0)
    serious_error("Stat");

  printf("File %s:  mode: %X  size: %ld  owner: %d\n",
    argv[1], buffer->st_mode, buffer->st_size, buffer->st_uid);

  exit(EXIT_SUCCESS);
}

Can someone help me solving this please ?

You need buffer to point to status. Or, you can just pass &status instead of passing buffer, and then use status.st_mode etc.

Hi Ramsis94.
You can just use status, but pass it's address like &status.

Code:

#define _DEFAULT_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
 
void serious_error(char *msg) {
  perror(msg);
  exit(EXIT_FAILURE);
}
 
int main(int argc, char **argv) {
 
  if (argc != 2) {
    fprintf(stderr, "Usage: get_stats FILENAME\n");
    return EXIT_FAILURE;
  }
 
  struct stat status;
  if (stat(argv[1], &status) < 0)
    serious_error("stat");
 
  struct passwd *pass = getpwuid(status.st_uid);
 
  const char *type = "other";
  if (S_ISREG(status.st_mode))
    type = "regular";
  else if (S_ISDIR(status.st_mode))
    type = "dir";
  else if (S_ISLNK(status.st_mode))
    type = "symlink";
 
  printf("File: %s  type: %s  mode: %o  size: %ld  owner: %s (%d)\n",
    argv[1], type, (unsigned)(0777 & status.st_mode), (long)status.st_size,
    pass->pw_name, status.st_uid);
 
  return 0; 
}

There is no advantage in that, in fact it just makes it more complicated, but you could say:

Code:

  struct stat status, *pstatus = &status;
 
  stat(argv[1], pstatus);
  printf("%ld", (long)pstatus->st_size);