PHP date format issue using strtotime()

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!

I think your problem has to do with when you subtract a month, you put it at 2011-02-29 which does not exist (feb 29th only exists in leap years - every 4 years). So date() is automatically translating it to March 1st. — CrayonViolent
– CrayonViolent, Commented Mar 28, 2011 at 18:47
@crayon - that makes sense - how do I fix this? as above, I would simply need to subtract 1 as an integer from m — pepe
– pepe, Commented Mar 28, 2011 at 18:49
hmm...well IMO this isn't really broken. "-1 month" happens to land on a day that doesn't exist. The next day is the 1st. That IS "-1 month". If you made it land on 02-28 instead, that's technically more than 1 month. You could instead use "-X days" to get it to place it on 02-28 but this is a matter of opinion (semantics), since not all months have the same amount of days. IOW to say "one month ago from today" is not exact time. To say "02-01" is 1 month ago from "03-01" ...that is to say, "1 month ago" = X days... X is not going to be same from month to month. — CrayonViolent
– CrayonViolent, Commented Mar 28, 2011 at 18:57
If the first of March is not acceptable for one month before March 29th, what is acceptable? — salathe
– salathe, Commented Mar 28, 2011 at 19:14
please see my update in OP - I do not need the new date to be one month earlier - only subtract 1 from month. thanks for pitching in. — pepe
– pepe, Commented Mar 28, 2011 at 19:27

Valerij · Accepted Answer · 2011-03-28 18:52:03Z

1

you might use

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

answered Mar 28, 2011 at 18:52

Valerij

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pepe Over a year ago

this solves the issue, because explode allow to simply subtract 1 from the month [1] -- thanks for helping

Shauna · Accepted Answer · 2011-03-28 19:11:10Z

0

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.

answered Mar 28, 2011 at 19:11

Shauna

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pepe Over a year ago

thanks @shauna -- please see my update on OP for clarification of what I needed

johnlemon · Accepted Answer · 2011-03-28 19:12:10Z

0

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/

edited Mar 28, 2011 at 19:12

answered Mar 28, 2011 at 18:47

johnlemon

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1 Comment

pepe Over a year ago

that seems right - do you have any suggestion to resolve this?

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