convert between timestamp and date time - php

Question

I tried this code,it will give me the right date but the time is not correct:
function convert_datetime($str) {
list($date, $time) = explode(' ', $str);
list($year, $month, $day) = explode('-', $date);
list($hour, $minute) = explode(':', $time);
$timestamp = mktime($hour, $minute, $year, $month, $day);
return $timestamp;
}
if(isset($_POST['submit']))
{
$datetime=$_POST['startdate'].' '.$_POST['start_hour'].":".$_POST['start_minute'];
$timestamp=convert_datetime($datetime);
echo "DateTime:".$datetime;
echo " ";
echo "Timestamp:".$timestamp;
echo " ";
$dateandtime = date("Y-m-d H:i", $timestamp);
echo "converted:".$dateandtime;
}
with input: 2013-1-21 21:51
I will get this out put
DateTime:2013-1-21 21:51 Timestamp:1358807073 converted:2013-01-21 22:24
so the order is not correct.and in the time part I have problem.How to fix this?

Answer 1

Use Datetime. It's much easier and more accurate:
$datetime = DateTime::createFromFormat("Y-m-d H:i", '2013-1-21 21:51');
echo 'Timestamp: ' . $datetime->getTimestamp() . PHP_EOL;
echo 'Datetime: ' . $datetime->format("Y-m-d H:i") . PHP_EOL;
Confirmed working

Answer 2

You are missing the seconds argument - see mktime on phpdocs. In your example seconds is being supplied the value 2013, which when added to the time alters the overall result.
function convert_datetime($str) {
list($date, $time) = explode(' ', $str);
list($year, $month, $day) = explode('-', $date);
list($hour, $minute) = explode(':', $time);
$timestamp = mktime($hour, $minute, 0, $year, $month, $day);
return $timestamp;
}
On a side note, php does have conversion functions built in. Try strtotime.

Answer 3

Put in a zero field for seconds when you are passing the time. I believe it is taking 2013 seconds and using it to add 2013/60 and using it to add 33 minutes to your time. I believe that mktime assumes current date for missing fields, which is why it is still getting 2013 for the year.