leading 0 in month parameter making wrong output

Question

Why the leading zero in the month parameter making wrong output?

echo date("Y-m-d", mktime(0, 0, 0, 09, 23, 2013));//output 2012-12-23
echo date("Y-m-d", mktime(0, 0, 0, 9, 23, 2013));//output 2013-09-23

Answer 1

From https://bugs.php.net/bug.php?id=55327:

Numbers with leading 0's are octal. 08 is an invalid value. See http://php.net/integer

If you prefix a number with a leading 0, it marks the number as Octal. The octal numeral system uses the digits 0 to 7. So, 08 and 09 doesn't exist and are invalid.

The second statement is correct, and that's the correct method:

echo date("Y-m-d", mktime(0, 0, 0, 9, 23, 2013));

Answer 2

We can make this parameter as a string and it will work.

Try this:

echo date("Y-m-d", mktime(0, 0, 0, '09', 23, 2013));//output 2012-12-23