get_query_var can’t work on the sidebar

get_query_var() would not return a value for ‘pagename’ unless you’ve actually passed a query in the url for ‘pagename’, like:

/?pagename=product

I assume this is not how your permalinks are set up. Anyway, you can also access the pagename (post/Page slug) through the $post object:

<?php
if( is_page() ) {
	global $post;
	echo $post->post_name;
}
?>

EDIT: Ok, not thinking clear tonight… Using:

<?php echo get_query_var('pagename'); ?>

would display the pagename on a Page when using custom permalinks that generate a url like:

/product/

for the ‘Product’ Page.

but if the url is(when click on old post):
https://URL/photos/photo/234243
function return “”

what is th solution?

Did you ever find a solution for this? I’m trying to pass a variable through the URL to a single.php in an iframe like:

home page has:
href="?p=<?php the_ID(); ?>?wh=1"

single.php has:
get_query_var("wh"); echo "wh=" . $wh;

I would expect it to show the variable 1 on the single.php page. But it doesn’t.