Here is a little function that does the opposite of the parse_str function. It will take an array and build a query string from it.

<?php

/* Converts an array of parameters into a query string to be appended to a URL.
 *
 * @return  string              : Query string to append to a URL.
 * @param   array    $array     : Array of parameters to append to the query string.
 * @param   string   $parent    : This should be left blank (it is used internally by the function).
 */
function append_params($array, $parent='')
{
    $params = array();
    foreach ($array as $k => $v)
    {
        if (is_array($v))
            $params[] = append_params($v, (empty($parent) ? urlencode($k) : $parent . '[' . urlencode($k) . ']'));
        else
            $params[] = (!empty($parent) ? $parent . '[' . urlencode($k) . ']' : urlencode($k)) . '=' . urlencode($v);
    }

    $sessid = session_id();
    if (!empty($parent) || empty($sessid))
        return implode('&', $params);

    // Append the session ID to the query string if we have to.
    $sessname = session_name();
    if (ini_get('session.use_cookies'))
    {
        if (!ini_get('session.use_only_cookies') && (!isset($_COOKIE[$sessname]) || ($_COOKIE[$sessname] != $sessid)))
            $params[] = $sessname . '=' . urlencode($sessid);
    }
    elseif (!ini_get('session.use_only_cookies'))
        $params[] = $sessname . '=' . urlencode($sessid);

    return implode('&', $params);
}

?>

Note that the function will also append the session ID to the query string if it needs to be.