Read from file into buffer (problem)

[Lior]

Hello all of you out there....

I have a file, lets say it has a size of 1MB
I need to encode each byte of the file!
If I use a loop from 1 to FileSize , It is damn slow!
I dont want the Processing-Time function to be linear like O(n).

But when I read everytime 2048 bytes into buffer declared as String * 2048, I need now to make everytime a loop running from 1 to 2048, so I get the same time problem.

You know what I mean, Lets say the file size is 10K,
So if I run a loop from 1 to 10240, its just the same to run 5 times a loop from 1 to 2K.

Any Ideas For Improving The Processing-Time?

[kedaman]

LIIIOR, wasn't it the man with the sheshbesh game?

You can open files in binary and get the whole file into a single variablelength string if you know what I mean

[MrShickadance]

use the Input Function and not the statement

like so:

Dim buffer As String * 2048

'' open the file here in binary mode

'' read in a buffer full
buffer = Input(2048, #1)

[kedaman]

Try using this one:

Property Get File(filename As String) As String
Dim fnum As Byte
    fnum = FreeFile
    Open filename For Binary As fnum
        File = Space(LOF(fnum))
        Get #fnum, , File
    Close fnum
End Property
Property Let File(filename As String, textstring As String)
Dim fnum As Byte
    If Dir(filename) <> "" Then Kill filename
    fnum = FreeFile
    Open filename For Binary As fnum
        Put #fnum, , textstring
    Close fnum
End Property

And here's an example of how to use it

Msgbox file("C:\autoexec.bat")
file("C:\autoexec.bat")=file("C:\autoexec.bat") & chr(13) & "echo Cool!!! This one will show up when you restart your computer" & chr(13) & "pause"
Msgbox file("C:\autoexec.bat")

[Lior]

Hey again...
Thanks for trying to help me, but guys, thats not what I wanted. I already know how to load the whole file into a buffer with the Input function and also with the Get statement. I think I just didnt explain the problem well enough. So here is the problem well explained:

It will be easier to explain if I give a practical example.
So let's say I wanna encrypt some file, with a primitive method, let's say I'll take each byte and rewrite it as the next byte in the ASCII table.

Let's say I have this simple code:

Dim ByteRead as Byte
Open "Source" for binary as #1
Open "Target" for binary as #2
  Do
    Get #1, ,ByteRead
    Put #2, ,Chr$(ByteRead+1)
  Loop Until Loc(1)=lof(1) 'Until End Of File
Close

In this example we see that the time that will to the program to be completed is dependent on the source file size.

If the Source file size is 10MB so the program will do 10*1024*1024 loops ! too much time !

Now, If I wont read byte after byte as I did, and I will read 2K of data each time using the Get statement, *I still need to access each byte! and make a loop from 1 to 2048 *

So I will try to ask it in short:
How can the program processing time not be dependent on the file size?
In other words,
How can I access and change each byte in a file individualy,
without running a loop from 1 To FileSize ?


Thanks for any help,
Lior, An Israeli Programmer.

[MrShickadance]

Well I think we know what you are trying to do. What we are saying is read a block of the file at a time. Modify that chunk in memory and write it out to a new file. Blocking is much faster than reading a byte at a time and writing back.

[Lior]

Thanks man...
I forgot that reading 10K in these 2 methods is not the same.
if I read 10K byte after byte so I make 10240 read statements, but if I paste 2K into a buffer, so I do only 5 read statements.

Thanks for reminding me this.