Open a file in memory then destroy.

[Chrispybee]

I would like to have the ability to open a file (any file, any size) and put it into memory (maybe allocated at an address?), Get the information from memory then destroy it from memory (free up memory).

Can this be done in VB6?

[dglienna]

Not sure that I understand, but you can read into a buffer. This is for a text file, and you can do similar things with a binary file.

Option Explicit
 
Private Sub Form_Load()
  Dim x As Integer, st As String
  Dim ff As Integer
  Dim strBuff As String
  Dim str() As String
  ff = FreeFile
  Open App.Path & "\to do.txt" For Input As #ff
    strBuff = Input(LOF(ff), ff)
  Close #ff
  ' ----------------- two ways to skin a cat --------------
  MsgBox "Lines = " & Len(strBuff) - Len(Replace(strBuff, vbCrLf, "x")) + 1
  ' -------------------------------------------------------
  str() = Split(strBuff, vbCrLf)
  MsgBox "There are " & UBound(str) + 1 & " lines in the file"
  For x = 0 To UBound(str)
    st = st & str(x) & vbCrLf
  Next x
  MsgBox st
End Sub

[RobDog888]

This is exactly what you want. It will allow you to choose a file and read it into an array in memory. Then optionall clear the array contents. The array is accessible from any procedure in your form for other use.

Option Explicit
'Add a CommonDialog Control to your toolbox and add to your form.
'Project > Components > Controls tab > select "MS Common Dialog Control" > click OK.
Private arArray() As String
 
Private Sub Command1_Click()
 
    On Error GoTo My_Error
    
    Dim strFilePath As String
    Dim strBuff As String
    
    With CommonDialog1
        .CancelError = True
        .DialogTitle = "Select a file"
        .InitDir = App.Path
        .ShowOpen
        strFilePath = .FileTitle
    End With
    
    Open strFilePath For Input As #1
      strBuff = Input(LOF(1), 1)
    Close #1
    
    arArray() = Split(strBuff, vbNewLine)
    'File contents remail in the array in memory until erased
    If MsgBox("Do you want to clear the array contents?", vbYesNo + vbQuestion) = vbYes Then
        Erase arArray
    End If
    Exit Sub
    
My_Error:
    If Err.Number = cdlCancel Then
        MsgBox "File Open Canceled", vbOKOnly + vbExclamation
    Else
        MsgBox Err.Number & " - " & Err.Description, vbOKOnly + vbExclamation
    End If
End Sub

[Chrispybee]

Hi RobDog888 - This is more like what I wanted. One question tho. How can I effectivly clear the

strBuff

from being stored after the file has been opened and the array has been generated? I hope you get what I'm on about???

Basically, I want to make sure that at the end of my applications, there's absolutly nothing being resident in memory when I've finished with Arrays, strings and all other variables..

[leinad31]

strbuff = "" at end of procedure is the variable is local to the procedure

[dglienna]

When you unload your form, all objects are destroyed, anyways.

[RobDog888]

Not always, but in this case, yes when the strBuff variable goes out of scope its cleared.

[Chrispybee]

Cheers guys. I just want to make my applications as efficient as possible.
I would like to get to this stage:

When you run your application, it will take around 1.5mb. You do some stuff (loading files, saving and displaying lots of forms and strings, arrays). Once this has been done, I would like to get my app down to the 1.5mb memory usage.

Does anyone know if this is possible???

[dglienna]

I've run into problems trying to read large files into a buffer, and had to resort to reading in line by line. If you read into an array, you can still erase it when you are done with it

[randem]

dglienna,

What kind of problems?

[dglienna]

With large files, I've had it crash while reading into the buffer.

[randem]

dglienna,

What code are you using for that?

[dglienna]

The code that I posted. I was reading in html dictionary files by letter, and had to read line by line for a couple of the letters.

[randem]

dglienna,

Yeah, That Input statement probably does it. Try this:

Private Function ReadFile(Filename As String, Contents() As Byte)
Dim FNum As Integer
 
    FNum = FreeFile
    On Local Error GoTo ErrorRtn
    Open Filename For Binary As #FNum
    If LOF(FNum) = 0 Then Close #FNum: Exit Function
    ReDim Contents(LOF(FNum))
    Get #FNum, , Contents(): Close #FNum
    
ExitRtn:
 
    Exit Function
    
ErrorRtn:
 
    MsgBox Err.Number & " - " & Err.Description, vbCritical, App.Title
    Resume ExitRtn
    
End Function

[dglienna]

I read in 83 bytes. How do I change it back into text to display it?

[randem]

dglienna,

Do a Join to convert to a string.

[randem]

dglienna,

83 bytes? Boy thats a large file.

[dglienna]

It's the principle. Just testing. Why doesn't this work?

Private Sub Command1_Click()
  Dim str() As Byte, out$
  out = ReadFile(App.Path & "\to do.txt", str())
  out = Join(str())
  MsgBox out
End Sub

[dglienna]

Can't figure it out...

[randem]

dglienna,

Sorry, Try this. It works. I forgot Join only works on string arrays.

[randem]

dglienna,

But be aware that the ReadFile routine does not do Tab conversions.

[dglienna]

Thanks. It was only a simple test, just to clarify what was needed. I see you used CopyMemory. All other samples I saw read directly into a string, which is why I was confused.

[randem]

dglienna,

Strings are limited to a max size (65535 I believe), however byte arrays are limited by available memory (can be virtually unlimited). So, converting to a string is not a very good idea. Very large text files should be put into a string array and processed that way. Non text files should be left in the byte array.

[dglienna]

I might have to use your sample in the future, unless I modify it a little more than I already did for my test. I see no problem with parsing the string after it's read into a byte array. Plus, you can process in chunks.

[randem]

dglienna,

Here's one that returns a string array.

[dglienna]

That really helped. I'll have to look at it tomorrow to study it, as it's getting late. Thanks. There appears to be a method to the madness of binary files.