the_excerpt not displaying

Question

I have a loop where I display all posts on the site, the problem is that the_excerpt is not being displayed. What am I doing wrong?

  <?php 
    $all_posts = get_posts(array('numberposts' => -1));
    $total_posts = count($all_posts);
    $posts_per_column = intval($total_posts / 3);
    $count = 0;
    $col = 1;
    foreach($all_posts as $post):
  ?>

  <!--post-->
  <div class='post' id='article<?php echo $count; ?>'>
    <div class='thumb'> 
      <a href='<?php the_permalink() ?>'>
      <!--todo: round thumb images and make them of variable height-->
      <?php the_post_thumbnail() ?>
      <?php 
        $cat = get_the_category(); 
        $cat_long = $cat[0]->cat_name;
        $cat_split = explode(' ', $cat_long); 
        $cat_short = strtolower($cat_split[0]);
      ?>
      </a>
      <span class='tag <?php echo $cat_short ?>'><?php echo $cat_long ?></span>
    </div>

    <div class='inner <?php echo $cat_short ?>'>
      <h2 class='entry-title'><a href='<?php the_permalink() ?>'><?php the_title() ?></a></h2>
    </div>
    <div class='entry-content'>
      <?php the_excerpt() ?>
    </div>
  </div>
  <!--end post-->

Answer 1

You need to be using setup_postdata

foreach($all_posts as $post):
    setup_postdata($post);
    // the rest of your loop

If you look at the docs for get_posts you will see that in all of the examples.

Answer 2

Change this:

<?php 
    $all_posts = get_posts(array('numberposts' => -1));
    $total_posts = count($all_posts);
    $posts_per_column = intval($total_posts / 3);
    $count = 0;
    $col = 1;
    foreach($all_posts as $post):
  ?>

to this:

<?php
    $all_posts = new WP_Query(array('posts_per_page' => -1));
    $total_posts = $all_posts->found_posts;
    $posts_per_column = intval($total_posts / 3);
    $count = 0;
    $col = 1;

    if($all_posts->have_posts()):
        while($all_posts->have_posts()):
            $all_posts->the_post();
?>

and at the end, you have somewhere endforeach. Remove it and put:

<?php
        endwhile;
    endif;

    wp_reset_postdata();
?>

That's the right way (in my opinion) how it is done - therefore you can't reach the bug with the $post variable like it's in your case. In your case, It's look like you just overrode global $post variable - I'm wondering how some of your "the_" tags worked and some didn't.