fatal Error undefined function switch_to_blog()

Question

Hello All!

I got this puzzling beginner issue. It's my first Multisite install, latest versions of all, no plugins, and when I am trying to use in a page template the switch_to_blog function, I get this :

Fatal error: Call to undefined function switch_to_blog() in /SITES/Sitename/wp-content/themes/themename/page.php on line 28

with line 28 : switch_to_blog(1);

I must do something wrong, but it looks the function itself is not installed, though the function's file is there (as it should be in any normal install).

Is there a way to cleanly create the function, declare it or activate it ? I tried copy the function switch_to_blog to functions.php, and there is does not complain but is not working (i got the article from the CURRENT blog). but then error make it stop to restore_current_blog(); with the same fatal error...

I don't know where to begin... what might help you understand the issue ? THANKS in advance.

G.

Answer 1

Some time ago, but i ran into exactly the same misbehavior.

Have your multisite activated and installed correctly.

Because WordPress is just loading the functions when a multisite is really active. Here the code from wp-settings.php file around line 137 on WP 6.1.1

if ( is_multisite() ) {
    require ABSPATH . WPINC . '/class-wp-site-query.php';
    require ABSPATH . WPINC . '/class-wp-network-query.php';
    require ABSPATH . WPINC . '/ms-blogs.php'; // <--- switch_to_blog() is in here!!
    require ABSPATH . WPINC . '/ms-settings.php';
} elseif ( ! defined( 'MULTISITE' ) ) {
    define( 'MULTISITE', false );
}

---

Here i found a long read tutorial which helped me a lot: https://multilingualpress.org/docs/how-to-install-wordpress-multisite/

But there should be alternatives findable anyway.