title: Fatal error: Call to undefined function mb_strlen()
body: <p>I'm trying to make a donation center which I use the source code from Totorialzine.</p>
  
  <p>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</p>
  
  <p>here is what I get when I submit the comment on the page when my visitors donate. </p>
  
  <pre><code>Fatal error: Call to undefined function mb_strlen() in /home/yoursn0w/public_html/livetv/premium/thankyou.php on line 14
  </code></pre>
  
  <p>and here is the code in the php file.</p>
  
  <pre><code>&lt;?php
  
  require "config.php";
  require "connect.php";
  
  if(isset($_POST['submitform']) &amp;&amp; isset($_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")&lt;2)
      {
          $error[] = 'Please fill in a valid name.';
      }
  
      if(mb_strlen($_POST['messageField'],"utf-8")&lt;2)
      {
          $error[] = 'Please fill in a longer message.';
      }
  
      if(!validateURL($_POST['websiteField']))
      {
          $error[] = 'The URL you entered is invalid.';
      }
  
      $errorString = '';
      if(count($error))
      {
          $errorString = join('&lt;br /&gt;',$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 = '&lt;a href="donate.php"&gt;You were added to our donor list! &amp;raquo;&lt;/a&gt;';
          }
      }
  }
  
  ?&gt;
  </code></pre>
  
  <p>I have my database in the phpMyAdmin uploaded completed</p>
  
  <p>here is where I follow the instruction of the installation</p>
  
  <p><a href="http://tutorialzine.com/2010/05/donation-center-php-mysql-paypal-api/" rel="noreferrer">http://tutorialzine.com/2010/05/donation-center-php-mysql-paypal-api/</a></p>