I'm creating a wordpress theme and I created a shortcode to show an abstract of a post (the first image, title, and link) from a post (by its ID). To do this, I created a function to get the first image of the post:

function get_image($id)
    global $post;
    $post = get_post( $id );
    $first_img = '';
    $output = preg_match_all('/<img.+?src=[\'"]([^\'"]+)[\'"].*?>/i', $post->post_content, $matches);
    $first_img = $matches[1][0];

    if (empty($first_img)) {
        $first_img = get_template_directory_uri() . '/img/no-photo.png';
    return $first_img;

I test this in my localhost (Windows with XAMPP: PHP 7.2, MariaDB 10.1.31) and works correctly. But in my server, the server shows me this message when i call the shortcode

<img src="<br />
<b>Notice</b>:  Trying to get property 'post_content' of non-object in <b>path_to_theme/shortcodes.php</b> on line <b>152</b><br />
<br />
<b>Notice</b>:  Undefined offset: 0 in <b>path_to_theme/shortcodes.php</b> on line <b>157</b><br />
https://lostiposdevino.com/wp-content/themes/theme_name/img/no-photo.png" alt="">

In other part of my theme, I created a post metabox, and when I tried to get the post with global $post ($post->ID, PHP gave me a similar error:

Trying to get property ID of non-object in ...

I solved this deleting the global post and use the function get_the_id()

I think my problem is with the global $post because I got a plugin for rich snippets, and now shows me this:

Notice: Trying to get property 'ID' of non-object in /wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 56

Thank You!

WP Version: Wordpress 5.2.1, OS: Debian 9 Stretch, Server: Nginx, PHP Version: PHP 7.3 fpm, DB: MariaDB: 10.1.26

  • 1
    When you're globalizing the post, you're getting the current post in the loop. But then you reassign your post variable with get_post function and another post ID. When you get this error, it means that $post is not a post object, it maybe a WP_Error class which at first, you can check that. – Amirition May 22 '19 at 10:53
  • First of all, thanks for your answer. I'll check soon your troubleshooting. In case that you're correct. How can I solve this, maybe resetting the loop? Thanks again – Max May 22 '19 at 16:21
  • If you're using this shortcode in a place that post exists, then you should not reassign a global variable. It's better to create another variable if you want to get another post. But if you're not using the shortcode in the loop, then using a global variable is meaningless. Where you put your shortcode ? – Amirition May 22 '19 at 17:48
  • Effectively, I called the shortcode 3 or more times at a page, the first time, the global $post type (got with gettype()) is object, and the second call and all but first are NULL. – Max May 22 '19 at 23:11

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