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VB6 user defined types comparison

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VB6 user defined types comparison, How to evaluate if two sets of a user defined type are equal

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jens	6 Aug, 2008 - 04:31 AM Post #1
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	I have defined a datatype CODE Public Type palletType palletFileVersion As Integer typeOfPallet As Integer Assembly As assemblyType End Type assemblyType is also a type that I have defined. The definition is not of interest here why I omit it. Now, suppose I do this: CODE dim pallet1 as palletType dim pallet2 as palletType pallet1.palletFileVersion = 1 pallet1.typeOfPallet = .... 'And all other fields too pallet2.palletFileVersion = 1 pallet2.typeOfPallet = .... 'And all other fields too Later on in my code I want to know if the contents of pallet1 are the same as the contents of pallet2 so I do this: CODE If (pallet1 = pallet2) then.... 'Do somthing This (above) doesn't work! I get a "compile error, type mismatch" which points to the equal sign. How can I, if possible at all, compare the two sets of data without explicitly comparing each data field? Regards Jens
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PsychoCoder	6 Aug, 2008 - 06:46 PM Post #2
DIC.Rules == true; Joined: 26 Jul, 2007 Posts: 7,143 Thanked 50 times Dream Kudos: 7700 Expert In: VB, VB.Net, C#, SQL, ASP, ASP.Net, Web Development, HTML, CSS, Win32 API, Javascript, mySQL, J#, GDI My Contributions	Try using the Is keyword instead of a comparison operator. Something along the lines of vb If pallet1 Is pallet2 then.... 'Do somthing
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jens	7 Aug, 2008 - 02:19 AM Post #3
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	My problem is that my types are not objects (this is in VB6) and the help says QUOTE If object1 and object2 both refer to the same object, result is True; if they do not, result is False. Two variables can be made to refer to the same object in several ways. Also, if I understand the above correctly the Is thingy compares references while I want to do a "deep camparison" i.e. I want to compare all fields of my type. I guess I'll have to do it the hard way and compare field by field. Maybe I'm approaching this the wrong way. The task at hand is actually to determine wheter or not a user have changed any data in the data type or not. The user is presented with a screen where current data is displayed and has the option to change any data in the type by changing fields in a form. When done with the form the user presses "exit" or somthing like that. Right then I have to know (and take care) of any changes made. Could I somehow traverse the type with all its subtypes and make a checksum and compare checksum before with checksum after to know wheter or not data has changed? Other ideas? Thanks for your time! /Jens
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AdamSpeight2008

7 Aug, 2008 - 02:36 AM

Post #4

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   ' Enter the following Declare statement entirely as one, single line:
   Declare Sub hmemcpy Lib "kernel" (hpvDest As Any, hpvSource As Any,
      ByVal cbCopy As Long)

Public Type palletType
   palletFileVersion As Integer
   typeOfPallet As Integer
   Assembly  As assemblyType
End Type

   ' type2str converts a user-defined type variable to a string.
   Function type2str (t As myType) As String
      Dim s As String
      s = Space$(Len(t))
      Call hmemcpy(ByVal s, t, Len(t))
      type2str = s
   End Function


if type2str(pallet1)=type2str(pallet2) Then
 ' etc
endif

I claim not to have written to code as it was lifted straight from this page.
How to compare User-Defined Types In Visual Basic (Microsoft)

Edited Text: Select view plain to show the correct structure of the code. (Has been reported)

This post has been edited by AdamSpeight2008: 7 Aug, 2008 - 03:02 AM

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jens	7 Aug, 2008 - 05:11 AM Post #5
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	Thank you very much! With your information and MS Win32 replacement för hmemcopy which states that CODE Declare Sub CopyMemory Lib "KERNEL32" Alias "RtlMoveMemory" ( hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long) can be used with KERNEL32 instead of hmemcopy with KERNEL my problem is solved! Great! /Jens
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jens	7 Aug, 2008 - 07:51 AM Post #6
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	Unfortunately I was a little bit too quick in my judgement.... I started to make a snippet out of this but... As I tested this I found that changes in the string parts of the user defined type doesn't get detected. If I change any integer it's detected. Any clues? CODE '============================================================ ' The code below is for VB6 ' It is an example of how you can compare two variables of ' a user defined type to see if they contain the same data. ' (This can not be done by using "=" or "Is") ' Note that it works with nested user defined types! :-) ' You need one form and one module '============================================================ '============================================================ ' Put the following code in the main module, e.g. "Module1" '============================================================ ''============================================================ '' http://support.microsoft.com/kb/88551 '' http://support.microsoft.com/kb/129947/en-us '' This declaration is needed for the function type2str below '' to work. ''------------------------------------------------------------ Declare Sub mcpy Lib "kernel32" Alias "RtlMoveMemory" (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long) ''============================================================ '' Definition of user defined types ''------------------------------------------------------------ Public Type InnerTestType innerNumber As Integer innerString As String End Type Public Type TestType innerVar As InnerTestType outerNumber As Integer outerString As String End Type ''============================================================ '' Public Function type2str(indata As TestType) As String '' Converts a variable of the user defined type "TestType" '' to a string. ''------------------------------------------------------------ Public Function type2str(indata As TestType) As String Dim s As String s = Space(Len(indata)) Call mcpy(ByVal s, indata, Len(indata)) type2str = s End Function ''============================================================ '' Put the following code in the Form_Load event for your form ''============================================================ Private Sub Form_Load() Dim first As TestType Dim second As TestType first.innerVar.innerNumber = 11 first.innerVar.innerString = "Hello " first.outerNumber = 12 first.outerString = "all!" second = first If type2str(first) = type2str(second) Then MsgBox ("1: first = second") Else MsgBox ("1: first <> second") second.innerVar.innerNumber = 1 If type2str(first) = type2str(second) Then MsgBox ("2: first = second") Else MsgBox ("2: first <> second") second.innerVar.innerNumber = 11 If type2str(first) = type2str(second) Then MsgBox ("3: first = second") Else MsgBox ("3: first <> second") second.outerString = "Tjoppelibopp" If type2str(first) = type2str(second) Then MsgBox ("4: first = second") Else MsgBox ("4: first <> second") second.outerString = "all!" If type2str(first) = type2str(second) Then MsgBox ("5: first = second") Else MsgBox ("5: first <> second") Unload Me End Sub /Jens
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jens	7 Aug, 2008 - 08:05 AM Post #7
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	Seems like the string conversion doesn't work correctly. Anyone has any ideas of how to convert a user defined type to string or any other type (BLOB?) that can be compared in an easy way? /Jens
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AdamSpeight2008	7 Aug, 2008 - 08:45 AM Post #8
D.I.C Regular Joined: 29 May, 2008 Posts: 493 Thanked 31 times Dream Kudos: 1900 My Contributions	QUOTE(jens @ 7 Aug, 2008 - 04:05 PM) Seems like the string conversion doesn't work correctly. Anyone has any ideas of how to convert a user defined type to string or any other type (BLOB?) that can be compared in an easy way? /Jens It works for me.
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jens	7 Aug, 2008 - 01:12 PM Post #9
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	Have you tried my code (above)? These lines CODE second.outerString = "Tjoppelibopp" If type2str(first) = type2str(second) Then MsgBox ("4: first = second") Else MsgBox ("4: first <> second") should report "4: first <> second" but when I run it I get "4: first = second" Now I'm really lost. /Jens
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AdamSpeight2008	7 Aug, 2008 - 03:42 PM Post #10
D.I.C Regular Joined: 29 May, 2008 Posts: 493 Thanked 31 times Dream Kudos: 1900 My Contributions	QUOTE(jens @ 7 Aug, 2008 - 09:12 PM) Have you tried my code (above)? These lines CODE second.outerString = "Tjoppelibopp" If type2str(first) = type2str(second) Then MsgBox ("4: first = second") Else MsgBox ("4: first <> second") should report "4: first <> second" but when I run it I get "4: first = second" Now I'm really lost. /Jens I get the same as you. Know the cause now as well, would you like you like to know? The problem is caused by you defining in type with variable length string, by changing to fixed length it will work correctly. vb Public Type InnerTestType innerNumber As Integer innerString As String * 40 End Type Public Type TestType innerVar As InnerTestType outerNumber As Integer outerString As String * 40 End Type This will set the string to have a length of 40 characters.
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Ken Halter	7 Aug, 2008 - 09:42 PM Post #11
New D.I.C Head Joined: 18 Nov, 2007 Posts: 31 Thanked 4 times My Contributions	Try using LenB instead of Len to get the size of the UDT. CODE Dim ThisString As String ThisString = "This is a test" Debug.Print Len(ThisString), LenB(ThisString) 'the line above shows 14 (Len) and 28 (LenB) Strings became "hard to handle" with the introduction of Unicode (aka Unimess) As a last resort, you can use a byte array everywhere, instead of the string... but that requires changes thru-out (can be worth it in the long run) CODE Dim ThisString As String ThisString = "This is a test" 'then... sometime later.... Dim theByteArray() As Byte 'Create the byte array - one byte per character theByteArray = StrConv(ThisString, vbFromUnicode) 'whenever you need to, show the byte array as a string Dim ThatString As String ThatString = StrConv(theByteArray, vbUnicode) MsgBox ThatString, vbInformation 'I realize you're asking about UDTs but the process is the same, so...
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jens	8 Aug, 2008 - 12:10 AM Post #12
New D.I.C Head Joined: 9 May, 2008 Posts: 49 Thanked 1 times Dream Kudos: 50 My Contributions	Hello! Ken: Thank you for your time. Unfortunately the LenB thing didn't help and the other alternative you suggested would complicate my project too much. Adam: First of all: Thanks - I'm impressed. This made my day. Would you care to elaborate a little on the "* 40" part of your solution? I do understand that it changes from variable to fixed length but I've never seen this done like this before. I'll put the complete solution up at DIC as a snippet. /Jens
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