How to Pass Extra Variables in WordPress URLs?

Passing Extra Variables in WordPress URLs

When attempting to pass an additional variable in a WordPress URL, issues may arise when the URL contains additional information after the root domain. To resolve this, employ the following approach:

1. Utilizing WordPress Functions

Instead of interacting with superglobals, utilize the following WordPress functions:

• add_query_arg(): Creates a URL with the custom query variable.
• query_vars: Modifies WordPress's recognized query variables (applicable only on the front-end).
• get_query_var(): Retrieves the value of the custom query variable.

2. Example Implementation

On the page creating the link:

• Add the query variable to back-to-page link:

  <a href="<?php echo esc_url(add_query_arg('c', $my_value_for_c)); ?>"></a>

• Link to a different page:

  <a href="<?php echo esc_url(add_query_arg('c', $my_value_for_c, site_url('/some_other_page/'))); ?>"></a>

In your functions.php or plugin file (front-end only):

function add_custom_query_var( $vars ) {
  $vars[] = "c";
  return $vars;
}
add_filter( 'query_vars', 'add_custom_query_var' );

On the page retrieving and processing the query variable:

$my_c = get_query_var('c');

3. Back End Considerations

On the back end, the wp() function is not executed, so you cannot rely on the WP Query. Instead, inspect the $_GET superglobal:

$my_c = filter_input(INPUT_GET, "c", FILTER_SANITIZE_STRING);

By adhering to these recommendations, you can effectively pass additional variables in WordPress URLs, both on the front-end and back-end.

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