处理无限循环

Question

I'm trying to learn PHP programming through trial, error and lots and lots of practice. I've been working on a directory bases image gallery for the last few days and it seems to work fine. I can upload pictures and create new albums. Plus whenever I see a full size picture I have links to the previous and next pictures in the directory.

Now this is where I ran into problems. Once you got to the end of the directory the code would start an infinite loop while it searches for the next file, which isn't there.

So I altered my code and it now looks something like this:

$x = 1;
$dir = opendir($base.'/'.$get_album);
while ((($file = readdir($dir)) !== FALSE) && ($x == 1)) {
  while ($img < $file) {
    $img++;
    $image_exists = file_exists($base.'/'.$get_album.'/'.$img);
    if ($image_exists) {
      echo "<a href='member.php?album=$get_album&imgID=$img'>
              <img src='$base/$get_album/$img' width='70' align='right'>
            </a>";
      break;
    }
    $x++;
  }
}

This works when I get to the last picture in the directory. So I thought I'd do the same for when I get to the first picture and just invert the operators like so:

$x = 1;
$dir = opendir($base.'/'.$get_album);
while ((($file = readdir($dir)) !== FALSE) && ($x == 1)) {
  while ($img > $file) {
    $img--;
    $image_exists = file_exists($base.'/'.$get_album.'/'.$img);
    if ($image_exists) {
      echo "<a href='member.php?album=$get_album&imgID=$img'>
              <img src='$base/$get_album/$img' width='70' align='right'>
            </a>";
      break;
    }
    $x++;
  }
}

This however DOES NOT work. I can't understand why that would be the case and I've tried to change things around a few dozen times but I cant seem to make it stop looping.

What am I doing wrong?

Thanks in advance for your help (and for reading through all this).

Answer 1

The issue could likely be related to the fact that readdir returns a string, and you are treating it as if you know its a number. You might find that it is returning you something at the start or end, such as the parent directory '..' as a string or the current directory as a string '.'.

If you want to iterate over the directories, you should check that the return value from readdir is not '.' or '..' specifically.