wp_get_post_parent_id( int|WP_Post $post )

Source

File: wp-includes/post.php

function wp_get_post_parent_id( $post ) {
	$post = get_post( $post );
	if ( ! $post || is_wp_error( $post ) ) {
		return false;
	}
	return (int) $post->post_parent;
}