category class in single

I would like to put category class in single post. I searched the forum and found this:

add_filter('body_class','add_category_to_single');
function add_category_to_single($classes, $class) {
	if (is_single() ) {
		global $post;
		foreach((get_the_category($post->ID)) as $category) {
			echo $category->cat_name . ' ';
			// add category slug to the $classes array
			$classes[] = 'category-'.$category->slug;
		}
	}
	// return the $classes array
	return $classes;
}

When I put this in functions.php I get error:
‘ArgumentCountError thrown
Too few arguments to function add_category_to_single(), 1 passed in /home/vcsleen/domains/vcsleen.nl/public_html/wp-includes/class-wp-hook.php on line 288 and exactly 2 expected’

What am I doing wrong???

In same functions.php I use this:

// category id in body and post class
function category_id_class($classes) {
	global $post;
	foreach((get_the_category($post->ID)) as $category)
		$classes [] = 'cat-' . $category->cat_ID . '-id';
		return $classes;
}
add_filter('post_class', 'category_id_class');
add_filter('body_class', 'category_id_class');

Maybe that causes the error?

• This topic was modified 5 years, 4 months ago by inula.