Windows API: Passing Visual Basic DATE to COM objects 2006-12-16 -- Jim Kane >I need to send dates to a COM object that uses the VB DATEs. Does anyone
>know how to pass a value that populates as a DATE in VB.
>
> MSDN suggests using a DOUBLE* but these folks are locked into the 8 byte
> VB DATE type. I can populate the Clarion DATE, Longs, SQL Server
> DateTimes, etc just fine. I have tried formatted strings, starting and
> ending my date with #, passing as a DATETIME, as a Clarion Date, as a
> formatted LONG (D1, D2, D10, D17, same with dash at the end D10-) and
> nothing makes it through.
>
> I can find no reference to this in the Help or on the NG. (maybe I am
> searching in the wrong places)
Dates or date times are passed as either a Real or as a variant
In VB the datetime is the number of days since a 'base date' and the
fractional part is the time as a fraction of a day.
In other words:
vbdatediff Equate(36161)
ticksperday Equate(8640000)
VT_DATE Equate(7)
RealValue Real
CWDate Long
CWTime Long
To covert a clarion date to vb date ( no time ):
RealValue = CWDate-vbDateDiff
To add a time:
RealValue += ( CWTime -1 )/ TicksPerDay
To stuff it into a variant - you MUST use ole view to determine if a
variant or double ( real in clarion ) is expected.
variantreal Group
vt ushort
r1 ushort
r2 ushort
r3 ushort
realvalue real
End
clear( VariantReal ) !or variantinit()
VariantReal.VT = VT_date
VariantReal.RealValue = RealValue
Now pass the variant either by value ( as 4 long parameters ) or by
address - again OleView tells you which.
You can't do com without oleview.
I would caution you not to pass a date as a string without a lot of testing
to be sure the com object and you are using the same month-day order.
Some com objects change their settings for month-day based on the control
pannel settings, others are hard coded, and still others depend on the lcid
parameter passed if you are using IDispatch. I once tried to pass dates by
strings but I had this one customer for whom the code would fail. Long
story short the customer had a relative in Mexico so they changed the
control pannel setting to make IM and other stuff work better and then
forget to change it back. When my code ran while they were set to mexico
they'd get invalid date messages if it was after the 12th of the month.
The best way to control this and successfully pass a date as a string and
always have it work no matter what the users regional settings are is to use
VariantChangeTypeEX and pass a LCID parameter. See MSDN for that API if to
see how hit handles dates. Also be advised VariantChangeTypeEx is not
available on all OS - I think it's win95 it's not available on. Personally
I dont think it's worth the trouble to use the string method.
Jim Kane
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