php date add

Posted on 2016-08-30
Last Modified: 2016-08-31
One of those days when EVERYTHING goes wrong.

What is wrong with this:
$today = date('Y-m-d');
// 30 days out
$exp = date_add($today, date_interval_create_from_date_string('30 days'));
echo $exp;

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I get Warning: date_add() expects parameter 1 to be DateTime, string given in /home/backflow/public_html/date_add_test.php on line 4

What does it want, that IS date / time?
Question by:Richard Korts
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Expert Comment

ID: 41777368
Yes, you need to read the manual. date_add() Adds an amount of days, months, years, hours, minutes and seconds to a DateTime object, and returns another DateTime object. So param1, which is $today, should be a DateTime object, but it's a String.  (and it's returned as a String on line 2)

Expert Comment

ID: 41777370
If you want to create a DateTIme object from the date (is that even what you want?) you can try this: 

DateTime date_create ([ string $time = "now" [, DateTimeZone $timezone = NULL ]] )

             >  (Returns new DateTime object.)

What is it you are trying to do?

Expert Comment

by:Brian Tao
ID: 41777371
The date() function returns a date/time formatted string.  The date_add() function requires the first parameter to be a DateTime object rather than a date/time formatted string.
Use the following instead:
// procedural style
$today = date_create();
// or OO style
$today = new DateTime();

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Author Comment

by:Richard Korts
ID: 41777372
seems to me the "old fashioned" way is much easier.

1. Use mktime for time now.
2. multiply # of days by 86400.
3. add those seconds to time now
4. convert to date.

Assisted Solution

Donna earned 125 total points
ID: 41777376
if you omit timezone, it used the timezone on the server, yes.

You can try : echo $exp = date('Y-m-d', strtotime("+30 days"));

and you can use an if statement and a short variable ($i) to switch from 30 or 31 days, if you are looking for same day next month...
LVL 53

Accepted Solution

Scott Fell,  EE MVE earned 250 total points
ID: 41777390
$thirtyDays = date('Y-m-d', strtotime("+30 days"));
echo $thirtyDays;

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LVL 110

Assisted Solution

by:Ray Paseur
Ray Paseur earned 125 total points
ID: 41777394
seems to me the "old fashioned" way is much easier

"Easy" is relative and exists in a context.  I would hate to endure the complications of procedural code when I'm working with OO designs.  Date computations are like email - it seems like it ought to be easy, until you try to actually do it (right, Secretary Clinton?)

Assuming you can do date/time calculations yourself?  Don't do that.  Instead use the built-in PHP functions.  Your own computations, if you try to write them, will get incredibly complicated when you realize that twice a year (but only in some locations and not others), a day does not have 24 hours because of daylight-savings time.  Don't go there.  Instead follow the guidance that we already have written here at E-E.

These two articles show many of the same computations in parallel construction.  One gives the old procedural way; the other gives the modern object-oriented way.  You will find date addition and many other useful references in here.  Maybe bookmark them for future reference.

$future = date('c', strtotime('TODAY + 30 DAYS'));

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$alpha = new DateTime('TODAY');
$month = $alpha->add(new DateInterval("P30D"));
echo $month->format('c');

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Author Comment

by:Richard Korts
ID: 41778916
I used this:

$tnow = mktime (date("H"), date("i"), date("s"), date("n"), date("j"), date("Y"));
// 30 days out
$addsecs = 30 * 86400;
$t30 = $tnow + $addsecs;

Works perfect.

Seems like translating 30 days to seconds should work regardless of DST or Feb, 28 or 29 days, etc.

I used this in 2006 on a site, it still works.
LVL 110

Expert Comment

by:Ray Paseur
ID: 41778928
I used this in 2006 on a site, it still works.
You've been fortunate!  It's only going to be the wrong calculation when the script runs at a time that sends its reach across the DST change.  To my mind, that is one of the things that I know  can go wrong, and I don't want a call from an irate client at 2:00am when the time resets.  For me, it's just easier to "do it right."

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