ISO DATE FORMAT

When it comes to the date format on the Internet (not just in PHP), there is one ISO standard that you must know – ISO 8601. Well, here is the very compressed version to not bore people to tears:

• The year must be in the format of yyyy. For example, 1999.
• Year and month in yyyy-mm. For example, 1999-08.
• Full date in yyyy-mm-dd. For example, 1999-08-07.
• To represent the week of the year yyyy-Www. For example, 1999-W12.
• Date and time are in UTC yyyy-mm-ddThh:mm:ssZ. For example, 1999-08-07T12:34:56Z.
• To add a time zone yyyy-mm-ddThh:mm:ss+|-hh:mm. For example, 1999-08-07T12:34:56+04:00 or 1999-08-07T12:34:56-02:00.

That’s all for the common date formats. If you like to learn more about ISO 8601, I shall leave some links in the extras section below.

DATE TIME IN DATABASES

Please do take note that not all databases adopt ISO 8601 strictly. For example, MongoDB does adopt the ISO 8601 format quite rigorously, while MySQL only uses a “close enough” format to keep the date/time – yyyy-mm-dd hh:mm:ss (missing the “T” in the middle, and “Z” at the end). To get an ISO 8601 date/time from MySQL, we will need to do some yoga, and we shall walk through some examples below.

UNIX EPOCH TIME (UNIX TIMESTAMP)

This is another mystery you will find quite often in the cyber world, not just in PHP. Long story short, the Unix timestamp is the number of seconds that have elapsed since 1 Jan 1970 00:00:00 UTC. Yeah, it may sound silly and useless to some beginners right now, but it is actually very useful in calculations. For you guys who want to learn more, I will leave a link in the extras section below.

TIME

time() is one of the most basic time functions in PHP, and it gives you the current Unix timestamp. 

If you want to get the time one hour from now:

";

// 1 hour = 60 mins X 60 seconds = 3600 seconds
$later = $now + 3600;
echo "1 hour later - " . $later;
?>

DATE

To “convert” the Unix Timestamp into human-readable form, we can use the date(FORMAT, TIMESTAMP) function.

Please feel free to format the date as required, read the full list of how you can format the date here. But a gentle reminder that the timestamp is in UTC, use the date_default_timezone_set function if you need it in another time zone:

You can get the full list of supported Timezones here.

MKTIME

Apart from time(), there is a more… modular way to create Unix Timestamps – mktime(HR, MIN, SEC, MONTH, DAY, YEAR).

STRTOTIME

If you prefer a more human way to create the Unix Timestamps, use the strtotime(STRING) function:

";

$timestamp = strtotime("-1 hour");
$human = date("Y-m-d H:i:s", $timestamp);
echo "1 hour before - $human
";

$timestamp = strtotime("yesterday");
$human = date("Y-m-d H:i:s", $timestamp);
echo "Yesterday - $human
";

$timestamp = strtotime("2014-03-21 12:34:56");
echo "Date to timestamp - $timestamp
";
?>

This is probably one of the most useful functions, as it can even convert a date back to a timestamp. Read the PHP manual for the full list of what it can convert.

GET DATE

Lost track of a timestamp? Or only need certain parts of the date for processing? Use the getdate(TIMESTAMP) function:

TIME LOOP

Need to loop through the next couple of days for some calculations? Just use the for loop and good old elbow grease Mathematics.

";
}
?>

MYSQL TIMESTAMPS

Remember that timestamps are recorded in the format of yyyy-mm-dd hh:mm:ss in MySQL? We can actually use SQL to directly format the timestamp.

COMMON DATE FORMATS

Now for some common date formats.

";

// In ISO 8601 format
echo date("c", $timestamp) . "
";

// Human friendly form
echo date("j F Y, g:ia", $timestamp) . "
";

// Week number
echo date("Y", $timestamp) ."-W". date("W", $timestamp) . "
";
?>

DATE COMPARISON

DATE DIFFERENCE

format('%R%a days');
echo "$days difference between $dateA and $dateB";
?>

To compare 2 dates, we can use the date_diff(DATE, DATE) function, check out the PHP manual for a complete list on how to format the difference interval.

SUMMARY – ALL THE COMMON DATE/TIME FUNCTIONS

CHEAT SHEET

EXTRA REFERENCES

• ISO 8601 on Wikipedia
• Date and Time Formats on W3C
• Unix Epoch Time on Wikipedia

SOURCE CODE DOWNLOAD

Click here to download the source code, I have released it under the MIT license, so feel free to build on top of it or use it in your own project.
 

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