CodeIgniter form validation rules for checkbox

Question

I've a form with checkbox for accepting TOS. The problem is I need to add custom error for this checkbox,

    <form>

    <input type="text" name="fname" placeholder="Name" /><?php echo form_error('fname') ?>
    <input type="text" name="email" placeholder="Email" /><?php echo form_error('email') ?>
    <input type="text" name="password" placeholder="Password" /><?php echo form_error('password') ?>

    <input type="checkbox" name="accept_terms" value="yes" /> Accept TOS<br>
    <?php echo form_error('accept_terms') ?>

    </form>

PHP

<?php 

 $this->form_validation->set_rules('fname','First Name','trim|required|xss_clean');
 $this->form_validation->set_rules('email','Email','trim|required|xss_clean|valid_email');
 $this->form_validation->set_rules('password','Password','trim|required|xss_clean');
 $this->form_validation->set_rules('accept_terms','TOS','trim|required|xss_clean'); // Need to add custom error message 

if ( $this->form_validation->run() === TRUE ) {

}else{

}
?>

When the user does not select TOS, Then I have to say

Please read and accept our terms and conditions.

Note: I've added form_error function to display individual errors

Answer 1

I will do something like this,

if ($this->form_validation->run() === TRUE ) {
   if(!$this->input->post('accept_terms')){
      echo "Please read and accept our terms and conditions.";
      // Redirect
   }
}
else{

}

And for custom message you can call a custom validate function like,

$this->form_validation->set_rules('accept_terms', '...', 'callback_accept_terms');

And then set up this method in the controller:

function accept_terms() {
    if (isset($_POST['accept_terms'])) return true;
    $this->form_validation->set_message('accept_terms', 'Please read and accept our terms and conditions.');
    return false;
}