Question

I remember seeing somewhere using %D or something similar to declare constant where the value of %D is supplied while calling the constant.

define("EVENT_DATE","The event date is %D");

Any information on this, how does it work please?

Answer 1

Check out sprintf() and printf().

Example:

define('EVENT_DATE', 'The event date is %s.');
echo sprintf(EVENT_DATE, 'tomorrow morning');

The above will display:

The event date is tomorrow morning.

If all you want to do is print, and you’re absolutely sure that the string does not need htmlspecialchars() applied to it, then you can use printf() directly. It works just like sprintf(), but it echoes the result instead of returning it.

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As Mel points out while downvoting, %D is indeed a strftime() format. Check that out as well and check Mel’s example of how to use it.