php - date and time

Hello friends,

PHP is a great development platform for all kinds of websites. Its fast, robust and quite easy to learn. I have seen people master php on there own and then develop great dynamic systems for websites. Not only that PHP has a vast amount of ready made code available on the internet (for us illiterates its - Internate). Its opensource so any CMS or other framework based on it is mostly free. Plus the advantages of opensource always follow - for example a great huge number of users and developers. But for those of us who have just started taking baby steps in PHP, dates can be a great place to start.
PHP handles dates very effectively. From the epoch of unix time i.e. 1 January 1970 to a distant future, PHP can understand and reproduce dates quite smartly. It provides a lot of customization, be it converting date from timestamp or recognizing dates in different formats. But with such a flexibility PHP's date system also introduces some amount of confusion.
First the display system of date() function itself is really flexible. It uses a string format system. You pass a string like "d-m-Y" and its prints out "7-09-2011". That's so great, isn't it? But wait it would have been so simple if this was all. As i said, date() function uses string format system, so there are a whole lot of tokens that you can pass to it.
Here are all the tokens that you can pass. I have taken this table directly from
The following characters are recognized in the format parameter string
format character Description Example returned values
Day --- ---
d Day of the month, 2 digits with leading zeros 01 to 31
D A textual representation of a day, three letters Mon through Sun
j Day of the month without leading zeros 1 to 31
l (lowercase 'L') A full textual representation of the day of the week Sunday through Saturday
N ISO-8601 numeric representation of the day of the week (added in PHP 5.1.0) 1 (for Monday) through 7 (for Sunday)
S English ordinal suffix for the day of the month, 2 characters st, nd, rd or th. Works well with j
w Numeric representation of the day of the week 0 (for Sunday) through 6 (for Saturday)
z The day of the year (starting from 0) 0 through 365
Week --- ---
W ISO-8601 week number of year, weeks starting on Monday (added in PHP 4.1.0) Example: 42 (the 42nd week in the year)
Month --- ---
F A full textual representation of a month, such as January or March January through December
m Numeric representation of a month, with leading zeros 01 through 12
M A short textual representation of a month, three letters Jan through Dec
n Numeric representation of a month, without leading zeros 1 through 12
t Number of days in the given month 28 through 31
Year --- ---
L Whether it's a leap year 1 if it is a leap year, 0 otherwise.
o ISO-8601 year number. This has the same value as Y, except that if the ISO week number (W) belongs to the previous or next year, that year is used instead. (added in PHP 5.1.0) Examples: 1999 or 2003
Y A full numeric representation of a year, 4 digits Examples: 1999 or 2003
y A two digit representation of a year Examples: 99 or 03
Time --- ---
a Lowercase Ante meridiem and Post meridiem am or pm
A Uppercase Ante meridiem and Post meridiem AM or PM
B Swatch Internet time 000 through 999
g 12-hour format of an hour without leading zeros 1 through 12
G 24-hour format of an hour without leading zeros 0 through 23
h 12-hour format of an hour with leading zeros 01 through 12
H 24-hour format of an hour with leading zeros 00 through 23
i Minutes with leading zeros 00 to 59
s Seconds, with leading zeros 00 through 59
u Microseconds (added in PHP 5.2.2) Example: 654321
Timezone --- ---
e Timezone identifier (added in PHP 5.1.0) Examples: UTC, GMT, Atlantic/Azores
I (capital i) Whether or not the date is in daylight saving time 1 if Daylight Saving Time, 0 otherwise.
O Difference to Greenwich time (GMT) in hours Example: +0200
P Difference to Greenwich time (GMT) with colon between hours and minutes (added in PHP 5.1.3) Example: +02:00
T Timezone abbreviation Examples: EST, MDT ...
Z Timezone offset in seconds. The offset for timezones west of UTC is always negative, and for those east of UTC is always positive. -43200 through 50400
Full Date/Time --- ---
c ISO 8601 date (added in PHP 5) 2004-02-12T15:19:21+00:00
r RFC 2822 formatted date Example: Thu, 21 Dec 2000 16:01:07 +0200
U Seconds since the Unix Epoch (January 1 1970 00:00:00 GMT) See also time()
So that means using date('c') will give me "Wed, 7 Sept 2011 20:22:34 +0530". That's really awesome! also note that as i have mentioned before you can pass a custom format to this little function.
There are several functions in PHP that allow us to manipulate the dates as we wish. One such great function is strtotime(). It recognizes date and time. Yes, it can read the time if you pass it "Wed, 7 Sept 2011" and spit out the unix timestamp of that moment. This function in conjunction with date format allows us to convert date formats.
For example if we echo date('m-d-Y',strtotime('7/9/2011')); it prints out 9-7-2011. That's it. You have just changed format of a given time. What we are doing is using strtotime to recognize the timestamp at midnight of 7/9/2011. Then passing that timestamp as second parameter to date function. Wait, date() function takes second parameter? Yes, it takes a second parameter which should be an integer timestamp and if it is not given then our function smartly takes current timestamp as default and gives us current date.
There are another functions in PHP like mktime(), and time(). time() being the simplest one. It just returns current timestamp. mktime() on the other hand takes several parameters and returns the time stamp as per the parameters passed. mktime(), however can not recognize a string of date. It has to be given parameters in a specific formation
PHP also has a locale system. It can convert your time in to time of different time zones. So making a world clock application in PHP would be a great and really simple taks. Just go through this page at and use some of those functions wisely.
To wind it up, no one can argue that PHP has a really strong but at the same time confusing date/time architecture. What you do with it is up to your imagination. So what are you waiting for. Show me some of your imagination in the comments or mail me.

Amit Kriplani
PHP Web/Application Developer
Mobile: +91-9913932644
Skype: amitkriplani
Twitter: @amitk87