Using $_GET variables in the URL?

Question

I need to generate a simple error message on a page by passing a variable through the URL.

The URL is structured as follows:

http://site.com/parent-category/category/?error=pause

I'm sure it's the permalinks rewrite interfering, but I'm not sure how to resolve it.

Answer 1

Try adding the variable to the WordPress' array of 'recognised query variables'...

add_filter('query_vars', 'my_register_query_vars' );
function my_register_query_vars( $qvars ){
    //Add query variable to $qvars array
    $qvars[] = 'my_error';
    return $qvars;
}

Then the value of 'my_error' can be found via get_query_var('my_error'). (See Codex)

EDIT

From Otto's comment, it's better to do:

add_action('init','add_my_error');
function add_my_error() { 
    global $wp; 
    $wp->add_query_var('my_error'); 
}

Answer 2

This was the only way I could get this to work

add_action('init','add_query_args');
function add_query_args()
{ 
    add_query_arg( 'error', 'pause' );
}

http://codex.wordpress.org/Function_Reference/add_query_arg