Использовать системный вызов stat(2) для вывода на экран размера файла в байтах

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/sysmacros.h>
#include <time.h>
 
 
int
main (int argc, char *argv[])
{
  struct stat sb;
 
  if (argc != 2) {
    fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
    exit(EXIT_FAILURE);
  }
 
  if (stat(argv[1], &sb) == -1) {
    perror("stat");
    exit(EXIT_FAILURE);
  }
 
  printf("ID of containing device:  [%lx,%lx]\n",
     (long) major(sb.st_dev), (long) minor(sb.st_dev));
  printf("File type:                ");
 
  switch (sb.st_mode & S_IFMT) {
  case S_IFBLK:  printf("block device\n");            break;
  case S_IFCHR:  printf("character device\n");        break;
  case S_IFDIR:  printf("directory\n");               break;
  case S_IFIFO:  printf("FIFO/pipe\n");               break;
  case S_IFLNK:  printf("symlink\n");                 break;
  case S_IFREG:  printf("regular file\n");            break;
  case S_IFSOCK: printf("socket\n");                  break;
  default:       printf("unknown?\n");                break;
  }
 
  printf("I-node number:            %ld\n", (long) sb.st_ino);
  printf("Mode:                     %lo (octal)\n",
     (unsigned long) sb.st_mode);
  printf("Link count:               %ld\n", (long) sb.st_nlink);
  printf("Ownership:                UID=%ld   GID=%ld\n",
     (long) sb.st_uid, (long) sb.st_gid);
  printf("Preferred I/O block size: %ld bytes\n",
     (long) sb.st_blksize);
  printf("File size:                %lld bytes\n",
     (long long) sb.st_size);
  printf("Blocks allocated:         %lld\n",
     (long long) sb.st_blocks);
  printf("Last status change:       %s", ctime(&sb.st_ctime));
  printf("Last file access:         %s", ctime(&sb.st_atime));
  printf("Last file modification:   %s", ctime(&sb.st_mtime));
 
  exit(EXIT_SUCCESS);
}