如何使用codeigniter验证日期时间格式？

$this->form_validation->set_rules('departure_date', 'Departure Date', 'required');

I tried this above code. But the error message is not displaying.

in your controller you nned to use this:

$this->form_validation->set_rules('departure_date', 'departure_date', 'required|regex_match[\d{4}-(0[1-9]|1[0-2])-(0[1-9]|1[0-9]|2[0-9]|3(0|1))]');
$this->form_validation->set_message('required', 'Field required');
if ($this->form_validation->run() !== FALSE){
   //code if validation is correct
}

in your view:

<input type="text" name="departure_date"/>
<?php echo form_error('departure_date'); ?>

try to validate date (dd/mm/yyyy):

$this->form_validation
     ->set_rules('departure_date',
             'Departure date',
             'required|regex_match[\d{4}-(0[1-9]|1[0-2])-(0[1-9]|1[0-9]|2[0-9]|3(0|1))]');

or use regex for datetime :-

$exp = '/^([0-9]{4})([\-])([0-9]{2})([\-])([0-9]{2})[\ ]'
.'([0-9]{2})[\:]([0-9]{2})[\:]([0-9]{2})$/';

and your view for display error use form_error()

<input type="text" name="departure_date"/>
<?php echo form_error('departure_date'); ?>

For more :- CodeIgniter: Validate datetime field