VB6 - DOS Date/Time Conversions [Archive] - ForumsHQ

[syntax53]

DOS date and time stamps are stored as an integer, here are some functions I wrote to convert them.



DOS date to human readable date



Public Function DOSDate2Date(ByVal value As Long) As String

Dim BinaryDate As String, Month As String, Day As String, Year As String

Dim temp As String



If value = 0 Then GoTo NoDate:



BinaryDate = Dec2Bin(value)



If Len(BinaryDate) 10 Then GoTo BadFormat:



Year = Dec2Bin((Val(Right(value, 4) - 1980)))

Month = Dec2Bin(Val(Left(value, 2)))

Day = Dec2Bin(Val(Right(Left(value, 5), 2)))



If Len(Year) 7 Then Year = "1111111"

If Len(Month) > 4 Then Month = "1111"

If Len(Day) > 5 Then Day = "11111"



Date2DOSDate = Bin2Dec(Year & Month & Day)

Exit Function



NoDate:

Date2DOSDate = 0

Exit Function



BadFormat:

MsgBox "Incorrect Date format!", vbExclamation

Date2DOSDate = -1

Exit Function



error:

MsgBox "Incorrect Date format!", vbExclamation

HandleError

Date2DOSDate = -1

End Function





Human readable time to DOS time



Public Function Time2DOSTime(ByVal value As String) As Long

On Error GoTo error:

Dim BinaryTime As String, Hour As String, Minute As String, Second As String

Dim temp As String



If value = "00:00:00" Then GoTo NoTime:

If Len(value) 8 Then GoTo BadFormat:



Hour = Dec2Bin(Val(Left(value, 2)))

Minute = Dec2Bin(Val(Right(Left(value, 5), 2)))

Second = Dec2Bin((Val(Right(value, 2)) / 2))



If Len(Hour) 5 Then Hour = "11111"

If Len(Minute) > 6 Then Minute = "111111"

If Len(Second) > 5 Then Second = "11111"



Time2DOSTime = Bin2Dec(Hour & Minute & Second)

Exit Function



NoTime:

Time2DOSTime = 0

Exit Function



BadFormat:

MsgBox "Incorrect time format!", vbExclamation

Time2DOSTime = -1

Exit Function



error:

MsgBox "Incorrect time format!", vbExclamation

HandleError

Time2DOSTime = -1

End Function





Binary to Decimal conversion function (not written by me)



Public Function Bin2Dec(ByVal BinValue As String) As Long

Dim lngValue As Long

Dim x As Long

Dim k As Long



k = Len(BinValue) ' will only work with 32 or fewer "bits"

For x = k To 1 Step -1 ' work backwards down string

If Mid$(BinValue, x, 1) = "1" Then

If k - x > 30 Then ' bit 31 is the sign bit

lngValue = lngValue Or -2147483648# ' avoid overflow error

Else

lngValue = lngValue + 2 ^ (k - x)

End If

End If

Next x

Bin2Dec = lngValue

End Function





Decimal to Binary conversion function (not written by me)



Public Function Dec2Bin(ByVal mynum As Variant) As String

Dim loopcounter As Integer



If mynum >= 2 ^ 31 Then

Dec2Bin = "Number too big"

Exit Function

End If



Do

If (mynum And 2 ^ loopcounter) = 2 ^ loopcounter Then

Dec2Bin = "1" & Dec2Bin

Else

Dec2Bin = "0" & Dec2Bin

End If



loopcounter = loopcounter + 1



Loop Until 2 ^ loopcounter > mynum



End Function





Error Handler



Public Sub HandleError()



MsgBox Err.Source & vbCrLf & "Error " & Err.Number & ": " & Err.Description, vbExclamation



Err.Clear

End Sub

[Locke Cole]

I forget, but does VB support shift left and shift right operators? I'm pretty sure it supports binary 'and' and binary 'or'. But if it supports those, you can do the conversion much more simply (and faster) by using those rather than going from an integer to a string then back to integers.

[syntax53]

I forget, but does VB support shift left and shift right operators? I'm pretty sure it supports binary 'and' and binary 'or'. But if it supports those, you can do the conversion much more simply (and faster) by using those rather than going from an integer to a string then back to integers.

i believe you are right, but i'm not all too sure how and when to use 'and' in those ways. have a good doc on it?

[Locke Cole]

i believe you are right, but i'm not all too sure how and when to use 'and' in those ways. have a good doc on it?

Well the more important commands are shift left and shift right, you can mimic those by using division (to shift right by one, divide by 2, to shift right by two, divide by 4, to shift right by three, divide by 8, and so on) and multiplication (same scenario as division except you multiply by powers of 2).



I'll see if I can come up with something you could use as a guide of sorts.



Actually, here's the Date decoding code. I don't have routines that deal with the full 32-bit date/time integer as a whole, because in Delphi I split them into their seperate 16-bit component date and time parts. But still, you should get the idea. I've also included the ASM code that can be optionally used for completness sake--



procedure DecodeDOSDate(Date: word; var Year, Month, Day: word); register;

{$IFDEF PUREPASCAL}

begin

Year := ((Date and $FE00) shr 9) + 1980;

Month := ((Date and $1E0) shr 5);

Day := Date and $1F;

// perform some validation perhaps? Month is 4-bits, that allows for 0 to

// 15, and there are only 12 months

end;

{$ELSE}

asm

{ EAX Date }

{ EDX ^Year }

{ ECX ^Month }

{ [EBP+8] ^Day }

PUSH EBX



MOV EBX, Day

PUSH EAX

AND EAX, $0000FE00

SHR EAX, 9

ADD EAX, 1980

MOV [EDX], EAX

MOV EAX, [ESP]

MOV EDX, 1

AND EAX, $000001E0

SHR EAX, 5

JNZ @@1

MOV EAX, EDX

// CMOVZ EAX, EDX

@@1:

CMP EAX, 12

JNA @@2

MOV EAX, 12

@@2:

MOV [ECX], EAX

POP EAX

AND EAX, $0000001F

JNZ @@3

MOV EAX, EDX

// CMOVZ EAX, EDX

@@3:

MOV [EBX], EAX



POP EBX

end;

{$ENDIF}



Just look at the code between {$IFDEF PUREPASCAL} and {$ELSE}, that's the non-assembly Pascal code. As stated in the comments, there might be some arguement for some validation code-- especially if you use the month as an index into an array of 12 month names, if the value was outside the range of array elements you could conceivably end up with a run-time error.

[Locke Cole]

Actually, it probably looks better and makes more sense if it's syntax highlighted. I'll attach an image.

[zarus]

I was searching the web for a way to convert 16-bit DOS file date and time to conventional date and time when I came upon this thread. I've accessed files on my machine and observed the file name, dates, time etc. Dates and times are in 16 DOS format. I wrote a C code to convert the date and time to conventional format(using bit mask). However I cannot figure out how to do the reverse, conventional to DOS. Do you have a C version (not C++) of the above code ?.

The DOS file dates 12367 converted to 15/2/2004, and 11341 converted to 13/2/2002.

Thanks for your help.

:punch: