如何将数组元素的索引动态存储到变量中？

I'm trying to make a photo gallery with multiple galleries listed that I need to paginate.

So, this variable

$galleries = Photograph::find_by_sql($sql);

holds an array:

Array
(
[0] => Photograph Object
    (
        [id] => 
        [gallery_name] => candies
    )

[1] => Photograph Object
    (
        [id] => 
        [gallery_name] => icecream
    )

[2] => Photograph Object
    (
        [id] => 
        [gallery_name] => pastries
    )

[3] => Photograph Object
    (
        [id] => 
        [gallery_name] => chocolate
    )
)

(I've shortened it for convenience)

I'm using these two variables to set a selected gallery:

$newest_gallery = reset($galleries);
$gallery_name = (isset($_GET['subj']) ? $_GET['subj'] : $newest_gallery->gallery_name);

I was able to set the selected gallery by using the gallery_name, however, I'm unable to paginate the galleries since I need to somehow dynamically store a numerical index of an array element (which holds the gallery_name) into a variable in order to create the pagination function, since I need an integer value for this purpose. So, I basically need to get the index of an array element. Is there a way to do this?

If I understand your question correctly, you have to make a traverse over the array:

## subj is set - search for it in the array of the objects
if (isset($_GET['subj'])) {
  foreach ($galleries as $id => $gallery) {
    if ($gallery->gallery_name == $_GET['subj']) {
       ## we've found a match - note the id and the name
       $gallery_name = $_GET['subj'];
       $gallery_id =$id;
       break;
    }
  }
}
## if subj was not specified or we found no match in the array 
if (!isset($gallery_id)) {
  reset($galleries);
  $gallery_id = key($galleries);
  $gallery_name = $galleries[$gallery_id]->gallery_name;
}

Just loop through your array of galleries and add set the value for id yourself:

$i = 0;
foreach($galleries as $gallery){
    $gallery['id'] = $i;
    $i++;
}