使用strtotime（）的PHP日期格式问题

Question

I am using

$jsdate = date("Y, m, d", strtotime('-1 month', (strtotime($date))));

to convert my dates from

2011-03-28
to
2011, 02, 28

Problem is this is producing unpredictable results. For example today I got

2011-03-28
converted to
2011, 02, 28  // OK

 AND

2011-03-29
to
2011, 03, 01 // not OK!

Does anyone know what's wrong here? I wonder if the calculation is inaccurate because of the -1 month .

Is there a way of simply subtracting 1 from m in ...date("Y, m, d", ... ?

MORE INFO:

My data needs to be formatted as JavaScript Date Object in which January is 0, Feb is 1, etc. Therefore there is not a need to specifically subtract 1 month but actually subtract 1 from the month integer . At the end, the resulting string is not supposed to be 1 month earlier, but actually the same date, represented using JS Date Object style. I believe @vprimachenko's answer below is a good solution. I apologize if this wasn't clear in my OP.

Thanks!

Answer 1

you might use

$datee = explode('-',$date);
if($datee[1]-- < 0) {
    $datee[1]=12;
    $datee[0]--;
}
$jsdate = implode(', ',$datee);

Answer 2

strtotime might work in an unexpected way but it is logical

strtotime('-1 months',strtotime('2011-03-29')  // is 2011-02-29
date('Y-m-d','2011-02-29'); //gets converted to the next real date

Here is one kind of fix http://www.phpreferencebook.com/tips/fixing-strtotime-1-month/

Answer 3

The calculation isn't inaccurate, per se. There is no 2/29/2011. If you change your input to 3/29/2012, you'll see that it returns 2/29/2012, because 2012 is a leap year. The same would happen with using something like 7/31/2011. June only has 30 days, so July 31 minus one month would be July 1 (because June 31 doesn't exist).

You could just extract the month, subtract 1, and remake the date, but that will result in attempting to make dates that don't exist.

If you really need the corresponding day of the prior month, you'll probably need to do an if statement of something along the lines of the following to make the day roll back to the last day of February:

$jsdate = date("Y, m, d", strtotime('-1 month', (strtotime($date))));
if($month == '3') {
   $jsdate = date("Y, m, d", strtotime('-1 day', (strtotime($jsdate))));
}

You'll also have to account for the rest of the days in March that February doesn't have, as well as leap years, and do something similar for 31-day months that follow 30-day months.