[RESOLVED] Putting mixed data tyes to random access files

[el84]

I am familiar with using random access files, which I used extensively in the DOS (!) QBasic days. In Vb6 I use user defined types to lay out the bytes on disk to be allocated to various strings as in

Private Type DataBlock
Busname as String * 30
Tel As String *10
...
...
End Type

I'm quite comfortable storing strings to a random access file. My question is, if I wish to store say an Integer (2 Bytes) or a Long (4) on disk how do I convert it.
In QB it used to be MKI$ to write (put) and CVI to read (get). For the next up (Single) it used to be MKS$ to write and CVS to read. They were different as they took up 2 or 4 Bytes on disk, as applicable.
What is the syntax in VB6 for Byte, Boolean, Integer , Long and Single. (it can't be CStr as the Byte sizes on disk would be ambiguous and if the numeric data was scattered in the UDT type structure the offsets would be scrambled) to there must be a different syntax for each numeric type..

[Arnoutdv]

Just add them your type.
Using Put and Get of the type using binary File IO

[Arnoutdv]

Sample:

Option Explicit

Private Type tpVBForum
  sSubForum As String
  lNofPosts As Long
  lNofViewing As Long
End Type


Private Sub Command1_Click()
  Dim sFile As String
  Dim fID As Integer, i As Long
  Dim tVBForum() As tpVBForum
  
  ReDim tVBForum(1)
  tVBForum(0).sSubForum = "Visual Basic 6 and Earlier"
  tVBForum(0).lNofPosts = 1622132
  tVBForum(0).lNofViewing = 323
  tVBForum(1).sSubForum = "Mobile Development"
  tVBForum(1).lNofPosts = 1569
  tVBForum(1).lNofViewing = 8
  
  
  sFile = "c:\temp\vbforum.dat"
  If Len(Dir$(sFile)) > 0 Then Kill sFile
  
  fID = FreeFile
  Open sFile For Binary As #fID
    Put #fID, , CLng(UBound(tVBForum) + 1)
    Put #fID, , tVBForum
  Close #fID
End Sub

Private Sub Command2_Click()
  Dim sFile As String
  Dim fID As Integer, lNofRecords As Long, i As Long
  Dim tVBForum() As tpVBForum
  
  sFile = "c:\temp\vbforum.dat"
  
  fID = FreeFile
  Open sFile For Binary As #fID
    Get #fID, , lNofRecords
    ReDim tVBForum(lNofRecords - 1)
    Get #fID, , tVBForum
  Close #fID

  For i = 0 To lNofRecords - 1
    Debug.Print tVBForum(i).sSubForum, tVBForum(i).lNofPosts, tVBForum(i).lNofViewing
  Next i
End Sub

[el84]

Sorry Arnoutdv. Too long and complex to get my head round!
Although I do know how to add them to the type structure. But there must be another step
I'll simplify and rephrase the question. In QB to put a number to disk if it was say an Integer (2 Bytes long in the random file record structure) I would write say Bloggs$ = MKI$(number), and to read it I would write number = CVI(Boggs$).
I know from experiment that to read an integer from a random access file in Vb6 I need CInt(), but what is the keyword for write an integer to disk and how does it differ from Single, Long, Boolean etc which take different space?

[Arnoutdv]

It's just a simple Put and Get.
These methods take care of the correct handling of variables types used in the type definition.
There is absolutely no need for fiddling around with numbers to strings and vice versa.

Private Type DataBlock
  Busname as String * 30
  Tel As String *10
  SomeNumber As Integer
End Type

My code is just a basic example showing how to deal with an array of the UDT.
Fill the array
Write it disk
Read it from disk
Display the data

[el84]

Thanks for bearing with me. Do you mean that the Type declaration is enough? I found from experiment to need the conversion out (eg CInt) when I read. Mind you, that's when I read from old QB random access file. Perhaps I should experiment with a new Vb6 file?

[Arnoutdv]

The type declaration is enough
I have no experience with QB and/or it's random access files.
I would definitely try with a new file based on the VB6 methods.

[dilettante]

If you really have old data in files you need to bring forward to 1998 it might be safest to take the long road one time.

Use a compatible version of QB to read the data and export it as comma or tab delimited text. The use a VB6 program or even a short VBScript to import the text into a Jet database. All done.

There may have been conversion tools that shipped back around VB3 and earlier to deal with the old DOS data types. I doubt they are going to be easy to find 30 years later.

I just can't see any upside to screwing around with Random files at this late date, or even way back in 1998 when VB6 came out.

[Elroy]

Use a Variant in your UDT!

FYI: Variants take 16 bytes. And here's the complete list of the "types" of data they can store. However, in VB6, in the cases of Arrays, Objects, or Strings, they only store a pointer and not the actual data. In the cases of Byte, Integer, Long, Single, Double, Currency, LongLong, Date, & Decimal, they store the actual data inside the Variant. That's also true in the cases of storing a Null, Empty, and some of the other "indicator" values.

[Elroy]

Now, if you really need to read some of that old floating-point data from old files, here's the link that shows you how to do that which was already posted for you.

You don't need to worry about MKI/CVI, as Microsoft has stored an Integer (there was no Long) using 2s-complement basically forever. So those Integers read-and-write the same way they always did.

[el84]

[QUOTE=dilettante;5584069]If you really have old data in files you need to bring forward to 1998 it might be safest to take the long road one time.

..../QUOTE]

You've misunderstood my question. I have already successfully read all my QB random access files; that is not a problem. My question was in connection of how I should use variable on VB6 random access files in VB6.

[el84]

Now, if you really need to read some of that old floating-point data from old files, here's the link that shows you how to do that which was already posted for you.

As I explained in the previous post, my question was about using random access in future. I've dealt with all my previous apps.

[dilettante]

Using Random File Access

Look in the Reference section for the Open, Get, and Put statements for more details.

[el84]

Thanks all, and especially Arnoutdv. I have successfully tried all the data types, and all is well just with the type structure, as long as I remember to reserve the right number of bytes.

I'll now mark this resolved.

[DataMiser]

You don't even need to worry about the number of bytes in the type you can use the Len() function when you open the file.

Here is an example from an old VBDos program I wrote many moons ago

TYPE TOWNDATA
    wall AS STRING * 1
    Text AS INTEGER
    menu AS STRING * 1
    character AS STRING * 1
    bkcolor AS INTEGER
    forecolor AS INTEGER
END TYPE

Town in the line below is a reference to the type above

OPEN "CITY1.dat" FOR RANDOM AS #3 LEN = LEN(town)

By using Len(MyType) your record length will always be correct no matter what data types are in your UDT

[Episcopal]

Sample:

    Put #fID, , CLng(UBound(tVBForum) + 1)
    Put #fID, , tVBForum
  
    Get #fID, , lNofRecords
    ReDim tVBForum(lNofRecords - 1)
    Get #fID, , tVBForum

Get #fID, , lNofRecords ...

This is new to me, lNofRecords is returning the number of bytes, while (Get #fID, , tVBForum) is returning the data. One is Long and one is UTD..... entered in the same position and returning different values...

I read the msdn documentation that came with my VB6 but they didn't bring this explanation.

[Arnoutdv]

No, it’s about a long.
The first put statement writes a long, the first get statement reads a long