Virtual Arrays

[Dimster]

I was wondering if anyone has worked with Virtual Arrays? These are arrays which would reside on your hard drive rather than in ram or your computer memory. From what I recently read about them, they go back to an earlier time, circa 1980's, and were part of the Basic language. The worked along the lines of Files in terms that you would open and close them, use Input or Output and a number. So to declare them it would look something like this:

Dim #1, myArray(5000)
Open "myArray" for Input as #1

As I understand it, the virtual array enjoyed a random access feature and its size was only limited to the size of your hard drive or thumb drive.

And before you say it, I know if anyone responds to this enquiry you may be tipping off your age.

[bplus]

Yes Random Access is like arrays permanently stored in files. Back in 80's I stored prime numbers in a massive file, might have been first factor of every number don't remember which.

[Dimster]

Ya, I wonder what the difference would have been back then to work with either a File opened for Random access or a Virtual Array. I have multiple files which are constantly receiving updated data. They are pretty large now, can't imagen working with an array at the sizes of those files.

[Pete]

I coded the same back in the days where memory was at a premium. 2 + 2 is... wait for it.... 4

Pete

 - I'm not as old as the hills, but in all fairness, the hills are better looking.

[madscijr]

Yes Random Access is like arrays permanently stored in files. Back in 80's I stored prime numbers in a massive file, might have been first factor of every number don't remember which.

Each value would have to be written with the same number of bytes, right? 

Can someone who knows how to do random access files post an example?

[bplus]

Yes same amount of bytes for each record which could be divided into fields numeric type and/or fixed length strings.

We did setup an RA for Dictionary words and definitions for PhilOfPerth, simple word and definition per record, try search?

Oh I might have quickie example:

Code: (Select All)

_Title "UDT to Random Access File Test" ' b+ 2021-12-24
Type Image
    As String * 255 Text, FileName
    As Long SzX, SzY, PosX, PosY
End Type

Const SW = 1000, SH = 700
ReDim As Image TheItem(1 To 100), TheRecord

TheItem(1).Text = FakeText$(255)
TheItem(1).FileName = FakeText$(255)
Print TheItem(1).Text
Print Len(TheItem(1).Text)
Print TheItem(1).FileName
Print Len(TheItem(1).FileName)
Print "zzz"
Sleep

'make fake data to file
For i = 1 To 100
    TheItem(i).Text = FakeText$(255)
    TheItem(i).SzX = 100 + Rnd * 20
    TheItem(i).SzY = 70 + Rnd * 14
    TheItem(i).PosX = Rnd * (SW - TheItem(i).SzX)
    TheItem(i).PosY = Rnd * (SH - TheItem(i).SzY)
    TheItem(i).FileName = FakeText$(255)
Next

Open "Data Dump.RA" For Random As #1 Len = Len(TheRecord)
For i = 1 To 100
    'odious and tedious is this
    TheRecord.Text = TheItem(i).Text
    TheRecord.SzX = TheItem(i).SzX
    TheRecord.SzY = TheItem(i).SzY
    TheRecord.PosX = TheItem(i).PosX
    TheRecord.PosY = TheItem(i).PosY
    TheRecord.FileName = TheItem(i).FileName
    Put #1, , TheRecord
Next
Close #1
Print "Data File Ready"

' OK we got data filed! Now can we get it back
Open "Data Dump.RA" For Random As #1 Len = Len(TheRecord)
For i = 1 To 100
    Cls
    Get #1, i, TheRecord
    Print "Record Number:"; i
    Print "Text: "; TheRecord.Text
    Print "SzX:"; TheRecord.SzX
    Print "SzY:"; TheRecord.SzY
    Print "PosX:"; TheRecord.PosX
    Print "PosY:"; TheRecord.PosY
    Print "FileName:"; TheRecord.FileName
    Print " zzz..."
    Sleep
Next
Close #1

Function FakeText$ (lengthh)
    BlankString$ = Space$(lengthh)
    fini = Int(Rnd * 255) + 1
    For i = 1 To fini
        Mid$(BlankString$, i, 1) = Chr$(Rnd * (96 - 32) + 32)
    Next
    FakeText$ = BlankString$
End Function

[Dimster]

Hi Madscijr, here's some code which Steve drew up for me a while ago and it helped a lot, hope it's what you could be looking for.

Code: (Select All)

_Title "Random Access File Demo"

Type Person_Type 'a type to hold your records
    FirstName As String * 20
    LastName As String * 20
    Phone As _Unsigned _Integer64
End Type

Dim PhoneRecord As Person_Type 'and a variable to reference that type

Open "Phone Database" For Random As #1 Len = Len(PhoneRecord) 'open file at the length of one of those records.

Do
    Cls
    RecordLimit = LOF(1) \ Len(PhoneRecord) 'the number of records in your file.
    Print "Record"; Tab(5); "Last Name"; Tab(30); "First Name"; Tab(55); "Phone Number"
    For i = 1 To RecordLimit
        Get #1, i, PhoneRecord 'get the whole record
        Print i; Tab(5); PhoneRecord.LastName; Tab(30); PhoneRecord.FirstName; Tab(55); PhoneRecord.Phone
    Next
    Print
    Print "What to do: 1)Add a record"
    Print "            2)Delete a record"
    Print "            3)Edit a record"
    Print "            4)QUIT"
    Do
        a = Val(Input$(1))
    Loop Until a > 0 And a < 5
    Print a
    Print

    Select Case a
        Case 1 'add a record
            RecordLimit = RecordLimit + 1
            Print "Adding Record #"; RecordLimit
            Input "Enter Last Name:"; PhoneRecord.LastName
            Input "Enter First Name:"; PhoneRecord.FirstName
            Input "Enter Phone Number:"; PhoneRecord.Phone
            Put #1, RecordLimit, PhoneRecord
        Case 2 'delete a record
            Input "Which record to delete?"; DeleteRecord
            For i = DeleteRecord To RecordLimit - 1 'shift all records from deletion point on back one spot
                Get #1, i + 1, PhoneRecord
                Put #1, i, PhoneRecord
            Next
            Close #1
            a$ = Space$(Len(PhoneRecord) * (RecordLimit - 1)) 'soace for all but the last record
            Open "Phone Database" For Binary As #1
            Get #1, 1, a$ 'get the whole database (minus the deleted record)
            Close #1
            Open "Phone Database" For Output As #1: Close 'delete the old database
            Open "Phone Database" For Binary As #1 'save the new database to the drive.
            Put #1, 1, a$
            Close #1
            Open "Phone Database" For Random As #1 Len = Len(PhoneRecord) 'open file at the length of one of those records.
        Case 3 'edit a record
            Input "Which Record to edit?"; editrecord
            If editrecord > 0 And editrecord <= RecordLimit Then
                Print "Editing Record #"; editrecord
                Input "Enter Last Name:"; PhoneRecord.LastName
                Input "Enter First Name:"; PhoneRecord.FirstName
                Input "Enter Phone Number:"; PhoneRecord.Phone
                Put #1, editrecord, PhoneRecord
            Else
                Print "Invalid record number."
            End If
        Case 4 'system
    End Select

Loop

---

And oh yes, bplus also gave me a neat addition to this phone record demo where he explained how you could put a Random File within a Random File where I had been working with multiple additional entries like multiple phone numbers. I haven't found that example code but if this is what you are looking for I'll try to find that example as well?

[madscijr]

Yes same amount of bytes for each record which could be divided into fields numeric type and/or fixed length strings.

We did setup an RA for Dictionary words and definitions for PhilOfPerth, simple word and definition per record, try search?

Oh I might have quickie example:
...

Hi Madscijr, here's some code which Steve drew up for me a while ago and it helped a lot, hope it's what you could be looking for.
...
And oh yes, bplus also gave me a neat addition to this phone record demo where he explained how you could put a Random File within a Random File where I had been working with multiple additional entries like multiple phone numbers. I haven't found that example code but if this is what you are looking for I'll try to find that example as well?

Thanks to you both - this could come in handy!