Uncaught Error: Call to undefined function mb_strripos() [closed] - php

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I use plugin https://wordpress.org/plugins/facebook-auto-publish/ for Wordpress, but I got error Uncaught Error: Call to undefined function mb_strripos().
To check I've created single php file:
<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
echo mb_strripos("qwert", "w");
?>
And I got the same error. In php docs I didn't find what was wrong.
Output of php -v:
PHP 7.0.33-0ubuntu0.16.04.5 (cli) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
with Zend OPcache v7.0.33-0ubuntu0.16.04.5, Copyright (c) 1999-2017, by
Zend Technologies
Where is I'm mistaken? Thank you

Answer 1

You're using a plugin that's attempting to call a multibyte string function, mb_strripos(). The plugin isn't checking if those functions are available first however.
mbstring isn't a default extension in PHP. If you want to use those functions, you must install the extension first. Details on how to do that can be found in the documentation: https://www.php.net/manual/en/mbstring.installation.php
The approach you take to installation is going to depend on your hosting environment. It may be that you can install the extension yourself; it may be that you have to contact the hosting provider instead. Without knowing your particular setup, I can't make a suggestion.
The plugin really ought to be checking for mbstring support and showing a user friendly error message if it's not available rather than allowing it to trigger an error.