how can I include some custom variable from functions.php?

So, with my example, I should do this, right(?):

function my_global_vars() {

    global $myglobvar;
    $myglobvar= array(

        'mysite_address_url'  => get_query_var('http://my-site.com'),

    );

}
add_action( 'parse_query', 'my_global_vars' );

And what then?

Like this(?):
<?php echo($GLOBALS[‘mysite_address_url’]); ?>

And another question please, is it safe to use this globals?

And thank you for helping me!

I just tried it and it is not working.
I tried the above and did this in my index.php:
<a href="<?php echo($GLOBALS['mysite_address_url']); ?>">TEST</a>

and I got this instead:

<a href="<br />
<b>Notice</b>:  Undefined index: mysite_address_url in <b>/home/www/blablabla/wp-content/themes/blabla/index.php</b> on line <b>blabla</b><br />
">TEST</a>

Thanks, Andrew! It worked! But can you please tell me how safe is this to use global variables or there’s nothing to worry about it?

Thanks once again, Andrew!