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i'm writing an encryption program that separates a file into blocks...in which the number of blocks is in the form n ^ 2, so the number of bytes within each block are the length of the file / n ^ 2. I need to dim a variable for reading and writing bytes of a fixed length, which is the number of bytes within each block. i tried doing dim input1 as string * blocksize but that gave me an error saying that i needed a constant...not a variable. if there's any way to work around this, i'd really like to know. thx.
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Unfortunately, you can't dimention a fixed variable with the uknown size. You have to either use a number or a constant variable (also a number).
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but the thing is....the value of the blocksize variable does not change during the procedure....so i was wondering if there was any way to circumvent this, so that i could get the result that i wanted. it's not that the variable changes, it's just the result of a computation of 2 other variables which are both determined before the procedure using the blocksize variable is run. any ideas would be appreciated...
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I found the following code in vbworld articles written by Alex Allen.
Const ChunkSize = 1024
'This is the amount (chunk) of data to take each
'time the file is written to.
'The larger the quicker but more memory intensive.
'Here I have set it to 1024 bytes which equals 1KB.
Dim Data As String
Public Sub Form_Load
Open "c:\source" For Binary As #1 'Source
Open "d:\destination" For Binary As #2 'Destination
Do Until LOF(1) = Loc(1) Or EOF(1)
'Will do this loop until the end of the source file.
Data = ""
'Resets the size of the Data string.
MsgBox LOF(1) & vbTab & Loc(1) & _
vbTab & LOF(1) - Loc(1)
If LOF(1) - Loc(1) < ChunkSize Then
'If there is not enough data left for one chunk
Data = String(LOF(1) - Loc(1), 0)
'Sets the length of the string; Data.
Else
'If there is enough data left for one chunk
Data = String(ChunkSize, 0)
End If
Get #1, , Data
Put #2, , Data
Loop
End Sub
Click File\directory in the topic area and look for binary files.
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Here's an idea
Maybe you could do something like this. Let's say for the sake of this example, that you have a textbox containing text that you want to put into a file. Let's also say that the block size is unknown at compile time. What if you just take the length of the string in the textbox and divide it by the length of the block using the MOD operator (which gives you the remainder). If the remainder is 0, your string will divide equally into the block length and you are ok. If the remainder is more than 0, just pad the end of it with spaces to make it the correct size.
In this example, I used a big, multi-line textbox to input text. I used an input box to get the block length from the user (meaning it is unkown at compile time). The one wierd thing I had to do was double the block size when I opened the file, because VB uses 2-byte characters in it's strings (unicode) and the length argument in the Open statement must be in bytes, not VB characters.
It seems to work just fine. Here's the code:
Code:
Option Explicit
Private nBlockLen As Long
Private Sub Form_Load()
'Get block length from user
nBlockLen = CLng(InputBox("Enter block length below:"))
End Sub
Private Sub Command1_Click()
Dim nFileNum As Integer, _
nNumBlocks As Integer, _
nCounter As Integer
'If the text is not equally divisible by the block length to start
'with, then pad the end with spaces so it is evenly divisible
If Not (Len(Text1) Mod nBlockLen) Then
Text1 = Text1 & Space(nBlockLen - (Len(Text1) Mod nBlockLen))
End If
nNumBlocks = Len(Text1) / nBlockLen 'There will be no remainder now
nFileNum = FreeFile
'Since VB uses 2-byte per character strings, double block len
'There is probably a better way to do this part.
Open "c:\my documents\text.txt" For Random As nFileNum Len = nBlockLen * 2
Put #nFileNum, 1, Mid$(Text1, 1, nBlockLen)
For nCounter = 1 To nNumBlocks - 1
Put #nFileNum, nCounter + 1, Mid$(Text1, nCounter * nBlockLen, nBlockLen)
Next nCounter
Close #nFileNum
End Sub
Sorry if this is way off base, it was just an idea I had when I read your post.
~seaweed
