single.php - how to mark current page in the loop

Question

I am using the following loop on index.php.
The current viewed page would be one of the link in the loop.
How to make sure it is marked as current?

<ul id="questions" class="subpage">
      <?php 

          $index_query = new WP_Query( array( 'post_type' => 'faq', 'orderby' => 'modified', 'posts_per_page' => '-1', 'order' => 'DESC' ) );
          while ( $index_query->have_posts() ) : $index_query->the_post();

        ?>
      <li><a href="<?php the_permalink(); ?>"><?php echo get_field('short_version'); ?> &raquo;</a></li>
      <?php endwhile; ?>
    </ul>

get_field() is a function from Advanced Custom Fields and has the following format:

get_field($field_name, $post_id);

Answer 1

Here's a rewritten version of your code

<ul id="questions" class="subpage">
<?php 
$current_id = get_the_ID();

$index_query = new WP_Query( array( 'post_type' => 'faq', 'orderby' => 'modified', 'posts_per_page' => '-1', 'order' => 'DESC' ) );
while ( $index_query->have_posts() ) : $index_query->the_post();
    if(get_the_ID() == $current_id)
        echo 'this post has the same ID as the current global one';
    ?>
    <li><a href="<?php the_permalink(); ?>"><?php echo get_field('short_version'); ?> &raquo;</a></li>
<?php endwhile; ?>
</ul>

Please note that on the index.php you can have queries of single post types as well as of archives(depending on your theme). If in case of an archive this will match the first post of that archive only. If you want to match for other types of templates, please see the conditional tags

Answer 2

On a single.php page you should have a $post object, which is created by WordPress for those pages. $post->ID is the ID of the 'current' page. Compare that number against the IDs in your loop. If they match 'mark' you post.

Be aware: You may need to save $post to another variable to avoid clobbering it when you run your loop, or use $posts[0] instead of $post.