set_post_thumbnail() WordPress Function

function set_post_thumbnail( $post, $thumbnail_id ) {
	$post         = get_post( $post );
	$thumbnail_id = absint( $thumbnail_id );
	if ( $post && $thumbnail_id && get_post( $thumbnail_id ) ) {
		if ( wp_get_attachment_image( $thumbnail_id, 'thumbnail' ) ) {
			return update_post_meta( $post->ID, '_thumbnail_id', $thumbnail_id );
		} else {
			return delete_post_meta( $post->ID, '_thumbnail_id' );
		}
	}
	return false;
}
Uses	Description
wp-includes/functions.php:absint()	Convert a value to non-negative integer.
wp-includes/media.php:wp_get_attachment_image()	Get an HTML img element representing an image attachment.
wp-includes/post.php:update_post_meta()	Updates a post meta field based on the given post ID.
wp-includes/post.php:delete_post_meta()	Deletes a post meta field for the given post ID.
wp-includes/post.php:get_post()	Retrieves post data given a post ID or post object.
Used By	Description
wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php:WP_REST_Posts_Controller::handle_featured_media()	Determines the featured media based on a request param.
wp-admin/includes/ajax-actions.php:wp_ajax_set_attachment_thumbnail()	Ajax handler for setting the featured image for an attachment.
wp-admin/includes/ajax-actions.php:wp_ajax_set_post_thumbnail()	Ajax handler for setting the featured image.
wp-includes/post.php:wp_insert_post()	Insert or update a post.
wp-includes/class-wp-xmlrpc-server.php:wp_xmlrpc_server::mw_editPost()	Edit a post.
wp-includes/class-wp-xmlrpc-server.php:wp_xmlrpc_server::mw_newPost()	Create a new post.
wp-includes/class-wp-xmlrpc-server.php:wp_xmlrpc_server::_insert_post()	Helper method for wp_newPost() and wp_editPost(), containing shared logic.