more_extended.php

<?php
// カスタムフィールドの値 : for_all, need_loginで分岐
// set single.php
while ( have_posts() ) : the_post();

	$raw_content = get_extended( $post->post_content );
	$everyone_can_read_content = ! empty( $raw_content )
			? $raw_content['main']
			: get_the_content();
	$logged_in_can_read_content = $raw_content['extended'];

	if (
			$require_login === 'for_all'
			|| is_user_logged_in()
			||  ( $require_login === 'need_login' && empty( trim( $logged_in_can_read_content ) ) )
	) {

			the_content();

	} elseif (
			$require_login === 'need_login'
			&& ! is_user_logged_in()
			&& ! empty( trim( $logged_in_can_read_content ) )
	) {

			echo apply_filters( 'the_content', $everyone_can_read_content  );
			echo get_login_register_box();

	}

endwhile; // End of the loop.



// Box.
// set functions.php
function get_login_register_box() {

  $redirect = wp_get_referer() ? wp_get_referer() : home_url();
  $register_html = wp_register( '', '', false );
  $register_html = str_replace( '登録', '会員登録する', $register_html );
  $login_register_html = '';

  $login_register_html .= '<div class="login-register">';
  $login_register_html .= '<p class="login-register__title">会員登録が必要です</p>';
  $login_register_html .= '<p>これより先は会員限定コンテンツです。ログインまたは、会員登録が必要です。</p>';
  $login_register_html .= '<ul class="login-register__button-list">';
  $login_register_html .= '<li class="login-register__button-list_login">';
  $login_register_html .= '<a class="loginout_link" href="' . wp_login_url( esc_url( get_permalink( get_the_ID() ) ) ) . '">ログインする</a>';
  $login_register_html .= '</li>';
  $login_register_html .= '<li class="login-register__button-list_register login-register__button-list_button">';
  $login_register_html .= $register_html;
  $login_register_html .= '</li>';
  $login_register_html .= '</ul>';
  $login_register_html .= '</div><!-- /.login-register -->';

  return $login_register_html;

}