Return all category id's from single post

https://codex.www.ads-software.com/Function_Reference/wp_get_post_categories

where exactly did you get stuck with that Codex chapter?

what code have you tried?

alternatively, consider using get_the_category() https://codex.www.ads-software.com/Function_Reference/get_the_category

get_the_category() worked perfectly, thank you. For some reason I couldn’t get wp_get_post_categories() to work, no matter how I tried implementing it.

If anyone else is looking to do the same thing and use a specific post’s category ID’s as classes, here’s my code:

<?php
$categories = get_the_category();
$separator = ' ';
$classes = '';
if($categories){
   foreach($categories as $category) {
      $classes .= 'cat-'.$category->term_id.$separator;
   }
}
?>

<div class="<?php echo trim($classes, $separator); ?>">
   DIV CONTENT
</div>