Fatal error: Call to undefined function mb_strlen()

I'm trying to make a donation center which I use the source code from Totorialzine.

Everything works fine for me at this moment so far but the only problem I was struggling on and trying to look at for the whole day and can't figure what is actually wrong with the code exactly

here is what I get when I submit the comment on the page when my visitors donate. 

Fatal error: Call to undefined function mb_strlen() in /home/yoursn0w/public_html/livetv/premium/thankyou.php on line 14

and here is the code in the php file.

<?php


require "config.php";
require "connect.php";


if(isset($_POST['submitform']) && isset($_POST['txn_id']))
{
$_POST['nameField'] = esc($_POST['nameField']);
$_POST['websiteField'] =  esc($_POST['websiteField']);
$_POST['messageField'] = esc($_POST['messageField']);


$error = array();


if(mb_strlen($_POST['nameField'],"utf-8")<2)
{
$error[] = 'Please fill in a valid name.';
}


if(mb_strlen($_POST['messageField'],"utf-8")<2)
{
$error[] = 'Please fill in a longer message.';
}


if(!validateURL($_POST['websiteField']))
{
$error[] = 'The URL you entered is invalid.';
}


$errorString = '';
if(count($error))
{
$errorString = join('<br />',$error);
}
else
{
mysql_query("   INSERT INTO dc_comments (transaction_id, name, url, message)
VALUES (
'".esc($_POST['txn_id'])."',
'".$_POST['nameField']."',
'".$_POST['websiteField']."',
'".$_POST['messageField']."'
)");


if(mysql_affected_rows($link)==1)
{
$messageString = '<a href="donate.php">You were added to our donor list! &raquo;</a>';
}
}
}


?>

I have my database in the phpMyAdmin uploaded completed

here is where I follow the instruction of the installation

http://tutorialzine.com/2010/05/donation-center-php-mysql-paypal-api/

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最佳答案

The function mb_strlen() is not enabled by default in PHP. Please read the manual for installation details:

http://www.php.net/manual/en/mbstring.installation.php

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On Centos, RedHat, Fedora and other yum-my systems it is much simpler than the PHP manual suggests:

yum install php-mbstring
service httpd restart
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To fix this install the php7.0-mbstring package:

sudo apt install php7.0-mbstring
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For me, this worked in Ubuntu 14.04 and for php5.6:

$ sudo apt-get install php5.6-mbstring
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For me the following command did the trick

sudo apt install php-mbstring
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In case Google search for this error 

Call to undefined function mb_ereg_match()

takes somebody to this thread. Installing php-mbstring resolves it too.

Ubuntu 18.04.1, PHP 7.2.10

sudo apt-get install php7.2-mbstring
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PHP 7.2 Ubuntu 18.04

sudo apt install php-mbstring
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This worked for me on Debian stretch

sudo apt-get update
sudo apt install php-mbstring
service apache2 restart
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This question looks to be in relation to PHP on Unix. However, for anyone getting to this question for PHP on Windows, see https://www.php.net/manual/en/install.pecl.windows.php.

Since multi-byte string support is a core PHP extension, all that is necessary on Windows is to uncomment this line in your php.ini:

extension=php_mbstring.dll

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