---json
{
    "description": "What to do when you get this error: PHP Fatal error:  Uncaught Error: Call to undefined function mb_substr().",
    "dynamic_quality_monitoring": "false",
    "layout": "median",
    "low_quality_page": "false",
    "page_id": "xbwtk7anppg8qsunl5hdx",
    "title": "undefined function mb_substr(): what to do when you get this error ?"
}
---
====== ComboStrap - undefined function mb_substr()  ======


===== Problem =====
When [[howto:getting_started:1_dokuwiki|installing combostrap on the server]], the below error may occurs.

<console>
[Sat Jan 29 15:27:04.904342 2022] [php7:error] [pid 68063] [client 127.0.0.1:58960] PHP Fatal error:  Uncaught Error: Call to undefined function mb_substr() in /var/www/html/dokuwiki/lib/plugins/combo/ComboStrap/DokuPath.php:167
Stack trace:
  /var/www/html/dokuwiki/lib/plugins/combo/ComboStrap/DokuPath.php(226): ComboStrap\\DokuPath->__construct()
  /var/www/html/dokuwiki/lib/plugins/combo/ComboStrap/Page.php(247): ComboStrap\\DokuPath::createPagePathFromPath()
  /var/www/html/dokuwiki/lib/plugins/combo/ComboStrap/Page.php(271): ComboStrap\\Page->__construct()
  /var/www/html/dokuwiki/lib/plugins/combo/action/metalang.php(41): ComboStrap\\Page::createPageFromId()
  /var/www/html/dokuwiki/inc/Extension/EventHandler.php(81): action_plugin_combo_metalang->load_lang()
  /var/www/html/dokuwiki/inc/Extension/Event.php(72): dokuwiki\\Extension\\EventHandler->process_event()
  /var/www/html/dokuwiki/inc/Extension/Event.php(128): dokuwiki\\Extension\\Event->advise_before()
  /var/www/html/dokuwiki/inc/Extension/Event.php(195): dokuwiki\\Extension\\Event->trigger()
  /var/www/html/dokuwiki/inc/init.php(224): dokuwiki\\E in /var/www/html/dokuwiki/lib/plugins/combo/ComboStrap/DokuPath.php on line 167, referer: http://localhost/doku.php?id=start&do=admin&page=extension
</console>



===== Solution =====
The ''mb_substr'' function is part of the ''mbstring'' extension   and should be [[support:requirement#moduleextension|installed]].

This extension is installed on all hosted php server. If you are installing yourself your server, you should install all the extensions listed in the [[support:requirement#moduleextension|requirement page]].