Can't understand why sometimes a [caption] field appears

Question

I'm trying to make a php script which, given a post id, returns post content. I'm not the one who writes articles, I'm just operating on a wp site. Post content is for an app of mine which has to parse it.

My script is very simple:

<?php
    require_once("wp-load.php");
    if(isset($_GET['id'])){
           $post_id = $_GET['id'];
           $queried_post = get_post($post_id);
           echo $queried_post->post_content;
     }
 ?>

Result is the article but sometimes the image is embedded in a [caption] field, like this:

[caption id="attachment_78971" align="alignnone" width="276"]<a href="href" rel="attachment wp-att-78971"><img class="size-medium wp-image-78971"/></a>[/caption]

other times I have just the image

<img ...ecc 

why is that? Is there a way to force the same output regardless of who has written the article?

Answer 1

The [caption] part shows up because one of your authors/editors added a caption to the image when it was inserted into the post. You will have this problem not only with captions but with any other shortcodes that your authors/editors use. And you should be aware that WordPress includes several in its Core but various plugins and even themes provide a lot of them. You will need to process the shortcode:

echo apply_filters('the_content',$queried_post->post_content);

Or strip the shortcodes:

echo strip_shortcodes( $queried_post->post_content );

Which you do depends on the results that you want.

You should also be aware that echoing raw post content-- ie. $queried_post->post_content-- will probably not give you the formatting that you expect, because raw post content is not typically complete markup. Running the the_content filter, as above, sorts out most of that.

Answer 2

That’s a shortcode, and you should run …

apply_filters( 'the_content', $queried_post->post_content );

… before you print it out.

You cannot prevent users from using that from your script. And you should not.