Checking *any* date for validity?

[Robert E. Carneal]

Checking a fairly recent date for validity (that is, to make certain the date says "30 Jun 1922" and not "31 Jun 1922" or "30 Jum 1922") is fairly easy for years after 1900.

Before 1900, is there an easy way? For example, how would I verify that Feb 29, 1703 is a leap year? (Its not) Or that Apr 31, 1705 does exist? Right now, I add 2000 to the year to make it after 1900 and then check for validity. Is that the best way?

Thanks.

Robert



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[Tom Tallardy]

Robert -

not entirely clear on what you are trying to accomplish - however leap years are fairly simple:

if yr mod 4 = 0 it's a leap year
except
if yr mod 100=0 it's not a leap year
except
if yr mod 400=0 then it is a leap year

which I think works for everything as long as you are sticking to the current Gregorian calendar "stuff"

are you concerned strick about leap years?
the nbr of days in each month does not change except for leap year Febs...


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[Robert E. Carneal]

are you concerned strick about leap years?

Yes, but I am also concerned and trying to trap any invalid date.
31 Jun 1922
00 Dec 1955
99 Jul 1982
04 Fib 1944
31 Sep 1734
20 Sip 1982
07 10
Are all invalid dates.
All dates will be in format of dd Mmm YYYY.

I am aware the calendar changed, but I am going to stick with our present calendar system. Simplifies things.

Basically, what I am trying to do is come up with a formula in the least number of steps that checks to see if the date is valid.

Thanks.

Robert

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[Michael Mattias]

WinAPI function GetdateFormat handles SYSTEMTIME structures, which handle dates back to year 1600. If it errors out with ERROR_INVALID_PARAMETER the date is no good (assuming you test the function with good dates and it works ok there).

Oops, this is PB/DOS forum. WinAPI calls ain't gonna work. My bad.

However, I think there might be some BIOS interupt you can use...
Or maybe you could just..

FUNCTION isValidDate ( something) 
 LOCAL de AS INTEGER 

 ON LOCAL ERROR GOTO DateErrorTrap
 d$  =  DATE$  ' save current date 
 DATE$ "appropriate string representation of 'something'"
 DATE$  d$   ' restore 

 FUNCTION = (DE = 0)
 EXIT FUNCTION

DateErrorTrap:
 DE = 1  
 RESUME NEXT

END FUNCTION

[This message has been edited by Michael Mattias (edited July 24, 2007).]

[Tom Tallardy]

Robert -

pretty "simple" approach would be

Function pickaname (Dt$)
'presuming Dt$="dd mmm yyyy" input format

function=%true
Dt$=trim$(Dt$)

'optionally check format
if mid$(Dt$,3,1)<>" " then function=%false:exit function
if mid$(Dt$,7,1)<>" " then function=%false:exit function

day%=val(left$(Dt$,2))
if day%=0 then function=%false:exit function

febdays%=28
year%=val(mid$(Dt$,8))
if year% mod 4=0 then febdays%=29
if year% mod 400=0 then febdays%=29

month$=mid$(Dt$,3,3)
select case ucase$(month$)
case "FEB"
if day%>febdays% then function=%false
case "JUN","APR","SEP","NOV"
if day%>30 then function=%false
case "JAN","MAR","MAY","JUL","AUG","OCT","DEC"
if day%>31 then function=%false
end select

end function

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[Michael Mattias]

You'll have to remove or change one line, but the DATEUNIT.BAS file supplied with the PB/DOS 3.5 compiler contains a function cleverly named "VaidDate" you can use.