Helpful strtotime reminders

Jul 12, 2007 php

This post is more than 18 months old. Since technology changes too rapidly, this content may be out of date (but that's not always the case). Please remember to verify any technical or programming information with the current release.

Today, Todd (one of the consultants that (“the triangle”) uses) called me up to share a bit of a reminder and also tell me about an issue in the code that was in one of our older modules. There was an issue with the strtotime function converting a year to a timestamp.

I thought I’d take a few minutes to just outline strtotime() examples again, as a reminder:

strtotime() is a useful function that converts english based strings to unix timestamps. These can range from iso date formats 2007-07-11 to proper written dates July 11th, 2007 to descriptive range based dates +3 days. The output is always a unix timestamp compatible with the date() functions. While the manual doesn’t give all the possible combinations, it does give some useful examples. Well, in order to test and predict the behavior of this tool, I tried out a few more date combinations to see what would happen.

print "date('r', strtotime('now'))";
print date('r', strtotime('now'));
print "<hr></hr>";

print "date('r', strtotime('+1 day'))";
print date('r', strtotime('+1 day'));
print "<hr></hr>";

print "date('r', strtotime('06/28/1983'))";
print date('r', strtotime('06/28/1983'));
print "<hr></hr>";

print "date('r', strtotime('6/28/83'))";
print date('r', strtotime('6/28/83'));
print "<hr></hr>";

print "date('r', strtotime('6/1999'))";
print date('r', strtotime('6/1999'));
print "<hr></hr>";

print "date('r', strtotime('1999'))";
print date('r', strtotime('1999'));
print "<hr></hr>";

This was the output: (with php 5.2)

date('r', strtotime('now'))Wed, 11 Jul 2007 19:05:18 -0500

* * *

date('r', strtotime('+1 day'))Thu, 12 Jul 2007 19:05:18 -0500

* * *

date('r', strtotime('06/28/1983'))Tue, 28 Jun 1983 00:00:00 -0500

* * *

date('r', strtotime('6/28/83'))Tue, 28 Jun 1983 00:00:00 -0500

* * *

date('r', strtotime('6/1999'))Wed, 31 Dec 1969 18:00:00 -0600

* * *

date('r', strtotime('1999'))Sun, 11 Jul 1999 19:05:18 -0500

* * *

Let’s check out the important things here: As predicted, most of the results came out accurately. Now came out as exactly today’s date and time. +1 day came out as one day (24 hours) exactly in the future. mm/dd/yyyy and m/dd/yy formats come out as expected with a proper date but a zero time. m/yyyy was not properly interpreted (which makes sense, how do you know if that’s a month or a day…). Finally, the plain year came out as that year’s version of today’s date - which is kind of helpful (in case you wanted to know what day july 11th was back in 1999).

I wasn’t entirely certain of the second from last result however. I did a quick check, however… date('r', 0) comes back as the same time - so that’s the proper value for a zero - or unknown date.

Another cool note is that for versions of PHP less than 5.1, they did not support a negative timestamp on windows and some *nix distros. My version on windows have moved pass this limitation though:

print date('r', -100);

The output:

Wed, 31 Dec 1969 17:58:20 -0600

As always, there is a wealth of knowledge in the comments on the PHP manual page.