Source

File: wp-includes/post-template.php

function get_the_title( $post = 0 ) {
	$post = get_post( $post );

	$title = isset( $post->post_title ) ? $post->post_title : '';
	$id    = isset( $post->ID ) ? $post->ID : 0;

	if ( ! is_admin() ) {
		if ( ! empty( $post->post_password ) ) {

			/* translators: %s: Protected post title. */
			$prepend = __( 'Protected: %s' );

			/**
			 * Filters the text prepended to the post title for protected posts.
			 *
			 * The filter is only applied on the front end.
			 *
			 * @since 2.8.0
			 *
			 * @param string  $prepend Text displayed before the post title.
			 *                         Default 'Protected: %s'.
			 * @param WP_Post $post    Current post object.
			 */
			$protected_title_format = apply_filters( 'protected_title_format', $prepend, $post );
			$title                  = sprintf( $protected_title_format, $title );
		} elseif ( isset( $post->post_status ) && 'private' === $post->post_status ) {

			/* translators: %s: Private post title. */
			$prepend = __( 'Private: %s' );

			/**
			 * Filters the text prepended to the post title of private posts.
			 *
			 * The filter is only applied on the front end.
			 *
			 * @since 2.8.0
			 *
			 * @param string  $prepend Text displayed before the post title.
			 *                         Default 'Private: %s'.
			 * @param WP_Post $post    Current post object.
			 */
			$private_title_format = apply_filters( 'private_title_format', $prepend, $post );
			$title                = sprintf( $private_title_format, $title );
		}
	}

	/**
	 * Filters the post title.
	 *
	 * @since 0.71
	 *
	 * @param string $title The post title.
	 * @param int    $id    The post ID.
	 */
	return apply_filters( 'the_title', $title, $id );
}