WordPress error when creating custom menu

I want to add a custom menu to WordPress
Method:
Step 1: functions.php

<code>if (function_exists('register_nav_menus')){
    register_nav_menus( array(
        'nav1' => __('网站导航1'),
        'nav2' => __('网站导航2'),
        'nav3' => __('网站导航3'),
    ));
}
function wp_nav1_menu($class='nav1', $location='nav1'){
    echo '<ul class="'.$class.'">'.str_replace("</ul></div>", "", preg_replace("/<div[^>]*><ul[^>]*>/", "", wp_nav_menu(array('theme_location' => $location, 'echo' => false)) )).'</ul>';
}
function wp_nav2_menu($class='nav2', $location='nav2'){
    echo '<ul class="'.$class.'">'.str_replace("</ul></div>", "", preg_replace("/<div[^>]*><ul[^>]*>/", "", wp_nav_menu(array('theme_location' => $location, 'echo' => false)) )).'</ul>';
}
function wp_nav3_menu($class='nav3', $location='nav3'){
    echo '<ul class="'.$class.'">'.str_replace("</ul></div>", "", preg_replace("/<div[^>]*><ul[^>]*>/", "", wp_nav_menu(array('theme_location' => $location, 'echo' => false)) )).'</ul>';
}</code>

Step 2: page1.php

<code><?php wp_nav1_menu(); ?></code>

page2.php

<code><?php wp_nav2_menu(); ?></code>

page3.php

<code><?php wp_nav3_menu(); ?></code>

Step 3: Enter the management background to set the corresponding menu, and the front desk will display normally (the menu is created)

---

Problem:
When I followed the above steps to create nav4 on the page4.php page, the page error occurred:
Fatal error: Call to undefined function wp_nav4_menu() in /……/page4.php on line x

Reply content:

I want to add a custom menu to WordPress
Method:
Step 1: functions.php

<code>if (function_exists('register_nav_menus')){
    register_nav_menus( array(
        'nav1' => __('网站导航1'),
        'nav2' => __('网站导航2'),
        'nav3' => __('网站导航3'),
    ));
}
function wp_nav1_menu($class='nav1', $location='nav1'){
    echo '<ul class="'.$class.'">'.str_replace("</ul></div>", "", preg_replace("/<div[^>]*><ul[^>]*>/", "", wp_nav_menu(array('theme_location' => $location, 'echo' => false)) )).'</ul>';
}
function wp_nav2_menu($class='nav2', $location='nav2'){
    echo '<ul class="'.$class.'">'.str_replace("</ul></div>", "", preg_replace("/<div[^>]*><ul[^>]*>/", "", wp_nav_menu(array('theme_location' => $location, 'echo' => false)) )).'</ul>';
}
function wp_nav3_menu($class='nav3', $location='nav3'){
    echo '<ul class="'.$class.'">'.str_replace("</ul></div>", "", preg_replace("/<div[^>]*><ul[^>]*>/", "", wp_nav_menu(array('theme_location' => $location, 'echo' => false)) )).'</ul>';
}</code>

Step 2: page1.php

<code><?php wp_nav1_menu(); ?></code>

page2.php

<code><?php wp_nav2_menu(); ?></code>

page3.php

<code><?php wp_nav3_menu(); ?></code>

Step 3: Enter the management background to set the corresponding menu, and the front desk will display normally (the menu is created)

---

Problem:
When I followed the above steps to create nav4 on the page4.php page, the page error occurred:
Fatal error: Call to undefined function wp_nav4_menu() in /……/page4.php on line x