サムネの関数化

functions.php

----

function mythumb($size) {
if(has_post_thumbnail()) {
$postthumb = wp_get_attachment_image_src(get_post_thumbnail_id(), $size);
$url = $postthumb[0];
} else {
$url = get_template_directory_uri(). /'no-img.jpg';
}
return $url;
}

-----

index.php

<img src="<?php echo mythumb('medium'); ?>" alt="">