title: Unable to get checkboxes values in codeigniter-3
body: <p>I am using codeigniter 3.16 on an Ubuntu 14.04 server, with apache 2.6 and php 5.6. I have created a multipart form to upload several files and check (or not) a group of checkboxes. My view looks something like:</p>
  
  <pre><code>&lt;form id="creation_form" name="creation_form" class="form-horizontal" action="&lt;?=(isset($edit)?site_url('admin/Projects/edit/').$project-&gt;ID:site_url('admin/Projects/create'))?&gt;" method="POST" enctype="multipart/form-data"&gt;
  // ...
      &lt;?php foreach ($users as $user) { ?&gt;
      &lt;tr&gt;
         &lt;td&gt;&lt;input type="checkbox" name="users[]" value="&lt;?= $user-&gt;ID ?&gt;" &lt;?=(isset($edit) &amp;&amp; isset($project_users[$user-&gt;ID])?"checked":"")?&gt;/&gt;&lt;/td&gt;
         &lt;td&gt;&lt;?= $user-&gt;name ?&gt;&lt;/td&gt;
         &lt;td&gt;&lt;?= $user-&gt;surname ?&gt;&lt;/td&gt;
         &lt;td&gt;&lt;?= $user-&gt;email ?&gt;&lt;/td&gt;
      &lt;/tr&gt;
      &lt;?php } ?&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>My controller gets the values of the checked checkboxes with this code:</p>
  
  <pre><code>$users_ids = $this-&gt;input-&gt;post("users");
  if (!isset($users_ids) || sizeof($users_ids) == 0) {
      $error_msg = "Assign at least one user to the project";
  }
  </code></pre>
  
  <p>But it is returning nothing, <code>$users_ids</code> is empty no matters how many checkboxes I check, and I am recovering other inputs like texts and files correctly but not the checkboxes.</p>