How do I Pass Extra Variables in WordPress URLs?

Passing Extra Variables in WordPress URLs

In WordPress, you may encounter difficulties passing additional variables through URLs. For instance, trying to add "&c=123" to "/news" may only work for the root URL (www.example.com?c=123) but fail if the URL contains additional information (www.example.com/news?c=123).

To address this issue, WordPress provides three essential functions:

• add_query_arg(): Creates URLs with new query variables.
• query_vars filter: Modifies WordPress's publicly known query variables.
• get_query_var(): Retrieves the value of custom query variables in URLs.

Example:

. On the page where you create the link or set the query variable:

• To add a query variable to a link back to the current page:

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

• To add a query variable to a link to another page:

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

. In functions.php or a plugin file:

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

. On the page where you want to retrieve and use the query variable:

$my_c = get_query_var('c');

On the Back End (wp-admin)

When accessing the backend (wp-admin), the main WP Query is not executed, and thus query variables are unavailable. Instead, you should use the following approach:

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

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