seek.c

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

// Goal: What should this print?

#define FILE_NAME "foo"

void checkFD(int fd);
void checkOffset(off_t offset);

int main(int argc, char *argv[]) {
  off_t offset;

  int file1, file2;

  file1 = open(FILE_NAME, O_CREAT | O_WRONLY);
  checkFD(file1);

  offset = lseek(file1, 0, SEEK_CUR);
  checkOffset(offset);
  printf("file1 at open: %ld\n", offset);

  // push forward
  offset = lseek(file1, 100, SEEK_CUR);
  printf("file1 after lseek 100: %ld\n", offset);

  file2 = open(FILE_NAME, O_CREAT | O_WRONLY);
  checkFD(file2);

  offset = lseek(file1, 0, SEEK_CUR);
  printf("file1 after opening file2: %ld\n", offset);

  offset = lseek(file2, 0, SEEK_CUR);
  printf("file2 at open: %ld\n", offset);

  close(file1);
  close(file2);

  return 0;
}

void checkFD(int fd) {
  if (fd == -1) {
    printf("Error opening file\n");
    exit(1);
  }
}

void checkOffset(off_t offset) {
  if (offset == -1) {
    printf("lseek error\n");
    exit(1);
  }
}