WordPress post thumbnail url

Easy access to the WordPress post thumbnail URL.

function get_the_post_thumbnail_url($post_id, $size = 'thumbnail') 
{
    $src = wp_get_attachment_image_src( get_post_thumbnail_id($post_id), $size );
    return $src[0];
}

function the_post_thumbnail_url($post_id, $size = 'thumbnail') 
{
    echo get_the_post_thumbnail_url($post_id,    $size);
}