Custom Callback Validation Function to Achieve a Custom Error Message - php

Question

I have a CI form with a field requiring a decimal number. Currently when the field fails validation the user gets an unhelpful message. "The field must be decimal". This is a poor user experience for a user that feels they should be able to use a leading period. e.g. ".4". I am trying to create a Custom callback validation function to achieve a custom error message. Here is my controller (simplified)...
<?php
class Form extends CI_Controller {
function index()
{
$this->load->helper(array('form', 'url'));
$this->load->library('form_validation');
$this->form_validation->set_rules('expenses', 'Expenses', 'trim|max_length[50]|callback_decimalcustom|xss_clean');
if ($this->form_validation->run() == FALSE)
{
$parent_data = array('country' => $countrydata, 'currency' => $currencydata, 'tour' => $tourdata, 'riders' => $ridersdata, 'measurement' => $measurementdata, 'tourdistance' => $tourdistance);
$this->load->view('myform', $parent_data);
}
else
{
$sql= array (
'expenses'=>$this->input->post('expenses'),
);
$ins = $this->db->insert('donations',$sql);
$this->load->view('formsuccess');
}
}
public function decimalcustom($str) //Custom decimal message
{
if (preg_match('/^[\-+]?[0-9]+\.[0-9]+$/', $str))
{
$this->form_validation->set_message('decimalcustom', 'The %s field is required in 0.00 format.');
return FALSE;
}
else
{
return TRUE;
}
}
}
?>
When testing, the error is not thrown, ever since I changed the validation from decimal to decimal custom. Am I missing something?

Answer 1

preg_match() returns TRUE when it's a valid number but you're trying to throw an error. Do the oposite.. (note the exclamation mark before preg_match)
if ( !preg_match('/^[\-+]?[0-9]+\.[0-9]+$/', $str) ) {
$this->form_validation->set_message('decimalcustom', 'The %s field is required in 0.00 format.');
return FALSE;
}
else {
return TRUE;
}