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  • Checking *any* date for validity?

    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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  • #2
    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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    Comment


    • #3
      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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      Comment


      • #4
        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..

        Code:
        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).]
        Michael Mattias
        Tal Systems Inc. (retired)
        Racine WI USA
        [email protected]
        http://www.talsystems.com

        Comment


        • #5
          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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          Comment


          • #6
            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.

            Michael Mattias
            Tal Systems Inc. (retired)
            Racine WI USA
            [email protected]
            http://www.talsystems.com

            Comment

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