Content filter won't work

Question

I'm trying to filter my content and on matches on flow I would like to change my html structure, but my rule doesn't really apply. I have the following filter which searches the first image of posts and on rule match attaching a css container. The preg_match_all is working but the str_replace doesn't

function imageFooter($content){

      global $post, $posts;

      preg_match_all('/<a.href="(.*?)"><img.*?src="(.*?)".*?><\/a>/', $post->post_content, $matches);
      $to_search = $matches[0][0];
      $replacement = '<div class="image_footer">'.$matches[0][0].'<span class="logo"></span></div>';
      str_replace($to_search , $replacement, $post->post_content);
      return $content;

    }

    add_filter('the_content',   'imageFooter');

Answer 1

Change,

str_replace($to_search , $replacement, $post->post_content);

to..

$content =  str_replace($to_search , $replacement, $post->post_content);

Answer 2

You haven't set $content to anything so it is just returning the same thing that was passed into the function. Read the doc's for str_replace. You should have:

$content = str_replace($to_search , $replacement, $post->post_content);

But why are you operating on $post->post_content? The post content is passed into the filter. You even have a parameter named $content that you aren't using. What you are doing is likely to cause trouble. Think about this.

Your site has 4 filters on the_content including yours.

1. Uses $content
2. Uses $content as modified by filter one, since they "chain".
3. Uses $content as modified by the previous two filters.
4. Your filter uses $post->content which is outside of the "chain". You've just wiped out all the preceding filters.

Also, you aren't using $posts at all.

Your code should be:

function imageFooter($content){
      preg_match_all('/<a.href="(.*?)"><img.*?src="(.*?)".*?><\/a>/', $content, $matches);
      $to_search = $matches[0][0];
      $replacement = '<div class="image_footer">'.$matches[0][0].'<span class="logo"></span></div>';
      $content = str_replace($to_search , $replacement, $content);
      return $content;
}

add_filter('the_content',   'imageFooter');

And you should be warned that using regex to parser HTML is very dicey business. It is easy to go wrong.