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GadgetGuy
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| Posted: December 01 2013 at 13:46 | IP Logged
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Having seen a number of questions over the years on the
forum about how to make DateTime functions work, I have
started writing a brief tutorial on their "care and
feeding" to help others understand, but in doing so have
run into a mystery myself.
The PH function "Today()" returns a value like...
09/26/2013 18:38:15:306
The function ph_relativedatetime(Today(),90) returns a
date/time value that is 90 minutes after the function is
executed, since Today() is equal to the moment the
function is run.
But ph_relativedatetime(12/01/2013 13:38:15:306,90)
returns a =SYNTAX ERROR=
The datetime value in the last example should be equal to
the example before it.
Unfortunately the forum only seems to contain examples
where Today() was used rather than a direct datetime
string.
Thus the question. Does ph_relativedatetime only work if
today() is used, or should it work with a fixed datetime
expression, or is this a bug?
Edited by GadgetGuy - December 01 2013 at 13:46
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GadgetGuy
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| Posted: December 01 2013 at 14:12 | IP Logged
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OK.
As sometimes happens, I can answer my own question.
[Well actually I got it wrong though. See Dave's answer
below.  ]
This works...
ph_relativedatetime(datetime("09/23/13 12:00:00"),30)
When a "datetime" value is required there is no way to
directly enter a value as it is an internal "system"
number of clock ticks that must be computed. Thus the
need to use the datetime() function.
Edited by GadgetGuy - December 02 2013 at 06:11
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dhoward
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| Posted: December 01 2013 at 19:16 | IP Logged
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Just to clarify a little further...
You can specify a literal date, time, or datetime by using the format of yyyy-mm-dd hh:mm:ss.fff
So for your example above, changing it to:
ph_relativedatetime(2013-12-01 13:38:15.306,90)
You'll get back the expected results...almost. The milliseconds portion will always be 0 as the ph_relativedatetime function truncates this value. If you want millisecond precision, you must use the ph_relativedtprecise function.
Now you may be asking why the function today() returns its output in mm/dd/yyyy hh:mm:ss format rather than the literal datetime input and its due to Windows formatting of datetime values and can be controlled by regional settings. So input is always yyyy-mm-dd hh:mm:ss.fff and output can vary (usually mm/dd/yyyy hh:mm:ss in the United States) based upon Windows regional settings.
Hope this helps,
Dave.
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GadgetGuy
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| Posted: December 02 2013 at 06:10 | IP Logged
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Dave-
Yesterday I tried your suggestion as one of the first
things, looking for alternatives, and could not get it to
work.
I tried slashes, dashes, commas, and blanks in about 20
different permutations/combinations and finally decided
direct datetime entry just wasn't possible. 
Copy/pasted your example from above this morning, and was
blown away when it worked!
Took me several minutes to finally figure out that the PH
datetime structure is year/month/day rather than
month/day/year. 
Thanks for the feedback. I just learned something!
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gg102
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| Posted: December 08 2013 at 09:54 | IP Logged
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If I may chime in on a similar, but not exact issue. I would love to have a date/time subtraction function. This would be used for situations like "The garage door has been open for xx minutes." or "Mike has been away for xx hours, yy minutes zz seconds".
Unless I'm missing something, the problem with the available functions is that they don't handle crossing a day boundary and using them is very clumsy for this purpose.
I can store now() when the garage door opens, and would love to subtract now() from that value when it closes.
Just something I'd like to have.
If anyone knows a way to do this, I'm all ears.
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GadgetGuy
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| Posted: December 08 2013 at 10:34 | IP Logged
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gg102-
Good idea, and as you have determined there is currently no way to do math on datetime values, other than "seconds after", etc(At least I haven't discovered such capabilities either.) [:-}
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gg102
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| Posted: December 08 2013 at 11:52 | IP Logged
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What I figured out to write to my log file was the following:
ph_writefile("{LOG_FILE_NAME}",0, today() + " Garage Door has closed. It has been open for: "+
string(int(int(secondsafter( time(mid("{GARAGE_DOOR_OPEN_SINCE}",11,9)),now()
)/60)/60)) +" Hours, " +
string(int(int(secondsafter( time(mid("{GARAGE_DOOR_OPEN_SINCE}",11,9)),now() )/60))-
(int(int(secondsafter( time(mid("{GARAGE_DOOR_OPEN_SINCE}",11,9)),now()
)/60)/60)*60 ))+ " Minutes, since: {GARAGE_DOOR_OPEN_SINCE}." + char(13) + char(10) )
Good luck in trying to figure it out.......
Thus, it sure would be nice to have a date/time subtract function.
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dhoward
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| Posted: December 08 2013 at 12:00 | IP Logged
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Concerning date subtraction, probably the best function for this is the ph_minutesafter function. It will take two datetime values and give you the difference in minutes (with decimal so you can also extract seconds). It will handle crossing date boundaries and if the first parm is greater than the second parm, you'll get a negative value.
In the meantime, I'll create a new function that allows you to extract hours, minutes, etc. from minutes.
Dave.
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gg102
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| Posted: December 08 2013 at 12:08 | IP Logged
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Thank you Dave.
Oh, Just to be sure:
I want to take a now(), save it, and later subtract it from now() and get a date/time. (duration)
Edited by gg102 - December 08 2013 at 12:14
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dhoward
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| Posted: December 08 2013 at 13:52 | IP Logged
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I took a stab at your formula and came up with:
ph_writefile("{LOG_FILE_NAME}",0,ph_rtne(ph_setvar_a(1,1,ph_ minutesafter(ph_getglobal_dt("GARAGE_DOOR_OPEN_SINCE"),today ()))) + string(today()) + " Garage Door has closed. It has been open for: " + string(ph_getvar_n(1,1) / 60,"#") + " Hours, " + string(ph_getvar_n(1,1) - truncate(ph_getvar_n(1,1) / 60,0) * 60,"#") + " Minutes, since:" + ph_getglobal_s("GARAGE_DOOR_OPEN_SINCE") + "~r~n")
Not sure if its really any easier or shorter but may lend some ideas until the new formula is available.
Dave.
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gg102
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| Posted: December 08 2013 at 17:45 | IP Logged
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Oh my, <SMILES>
Interesting twist, but with all respect Dave, it's just as obtuse, maybe a wee bit more.
Although, I think your routine will generate less heat in the CPU than mine. LOL
Thanks for the effort tho.....
I'll keep that one in the file for reference for now.
I think you'll agree now, it would be SO MUCH easier just to have a date/time subtraction (duration) function.
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Topic: DateTime functions
