日期时间的PHP setDate函数设置不同的日期

Question

I am learning to use PHP DateTime class and I came across the handy 'setDate' method. I tried to do the following to compare 2 dates:

$date = new DateTime();
$newDate = clone $date;
$newDate->setDate(2017, 08, 29);

if($date > $newDate){
    echo 'yes';

} else{
    echo "no";
}

According to the current date it shall return 'no' but it returned 'yes'. so I did a var_dump($newDate); and it returned:

object(DateTime)[2]
  public 'date' => string '2016-12-29 00:31:02.000000' (length=26)
  public 'timezone_type' => int 3
  public 'timezone' => string 'Europe/Zurich' (length=13)

It returned 2016-12-29 as the date which is not what I intended to set.

surely there something really wrong with what I am doing. Please help me find my mistake. Thanks

Answer 1

Instead of 08, it need to be 8 like below:-

<?php

$date = new DateTime();
$newDate = clone $date;
$newDate->setDate(2017, 8, 29);

if($date > $newDate){
    echo 'yes';

} else{
    echo "no";
}

Output:-https://eval.in/839909

Why:- As @Mark Baker tell correctly:-

Numbers prefixed with 0 in PHP are treated as octal, so 08 is octal 8, which is an invalid octal number, so treated as 0

And because of it you get yes as output:- https://eval.in/839910

You can check a number is octal or not like below:-

<?php

function is_octal($x) {
    return decoct(octdec($x)) == $x;
}

echo is_octal(08); // true

Output:- https://eval.in/839915 (the above code will work in php<7)