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Zohar Peled
Zohar Peled

Posted on • Originally published at

For the 1024 time – DateTime has no format!

(This is a shortened version of my most recent blog post)

This is probably one of the most frequent questions I see on stackoverflow:
How to change the date/datetime/time format.
This question comes all the time in the tags I’m following (c#, SQL Server, SQL etc’) and I’ll bet it comes frequently in any other tag as well.

I want to be as clear as I can about this: Date and time values have no concept of “format”. They are binary values, usually representing the number of time units since a specific epoch.

In C#, A DateTime value is the number of ticks (= 100 nanosecond) since Midnight, January 1st 0001 A.D in the Gregorian calendar, .

In Sql Server, different date and time data types are stored differently - but they are still basically stored as the integer value of a time unit since an epoch (datetime use 4 bytes for days since January 1st 1900 and 4 more bytes for the number of ticks (= 1/300 second) since Midnight - while DateTime2 has a far more sophisticated storage format to allow far grater accuracy and range) - but they are all basically working on the same principle - Store the number of units since an epoch.

Neither of these storage systems has the capability or need to store the display format of a DateTime value, and I’m guessing that in other technologies datetime values are probably stored in a similar manner.

Therefore, the concept of “format” is only relevant to date and time values when they are being displayed to us humans – as strings.

Top comments (2)

binarypatrick profile image

What about JavaScript 😝

peledzohar profile image
Zohar Peled

I have no idea. The last time I've written anything in Javascript was when JQuery was the new shiny framework - so my JS knowledge is not relevant for this decade...