如何防止和修复“Undefined offset：0 in”错误消息

Question

I have a function that is run in a WordPress plugin and when wp_debug is activated I receive this error message.

" Undefined offset: 0 in /…/wp-content/plugins/advanced-widget-pack/lib/advanced_widget_pack.class.php on line 568 "

Here is the function that is used in the plugin:

/**
 * Retrieves the image for a post
 *
 * Uses the post_thumbnails if available or
 * searches through the post and retrieves the first found image for use as thumbnails
 */
function featured_image_thumb($size = 50) {
    global $post;
    // If a featured image has been set, use the featured-thumbnail size that was set above with the class of 'thumb'
    if(has_post_thumbnail() ) {
        echo '<a href="'.get_permalink().'" title="'.get_the_title().'" >';
        the_post_thumbnail(array($size,$size),array('class' => 'thumb'));
        echo '</a>';
    }
    // If a featured image is not set, get the first image in the post content
    else {
        $first_img = '';
        ob_start();
        ob_end_clean();
        $output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
        $first_img = $matches[1][0];

        // Define a default fallback image in case a featured image is not set and there are no images in the post content
        if(empty($first_img)){
            $first_img = WP_PLUGIN_URL.'/advanced-widget-pack/images/nothumb.png';
        }

        // Generate the HTML code to display the image and resize the image with timthumb.php
        return '<a title="'.get_the_title().'" href="'.get_permalink().'"><img class="thumb" src="'.WP_PLUGIN_URL.'/advanced-widget-pack/timthumb.php?src=' . $first_img .'&w='.$size.'&h='.$size.'" alt="" /></a>';
    }
}

Line 568 or the place that the error is occurring is this section of the code:

$first_img = $matches[1][0];

I am not sure how to prevent or fix this error.

Any help or advise would be greatly appreciated. Thanks

Answer 1

Undefined offset $X[Y] means that the array X does not have a key Y. In your case $matches[1] does not have a first element.

I think you have to use a conditional :

if(preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches)){
  $first_img = $matches[1][0];
}

Answer 2

In my case an embracing with a conditional did it for me:

if( $output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches); )

All the Notices are gone! :)

Answer 3

Means that that first index of the array is not defined prob because the preg_match above it failed to find anything. You shouldnt have to worry about it really but putting the following after ob_end_clean should take care of it

 $matches[1][0] = '';