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Need help reading a file

I need a way to read the contents of a binary file up to a certain string of characters & then read x number of characters after that. Could someone kindly show me how? Thanks...

[182 byte] By [nbrege] at [2007-12-30]

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# 1

take a look at the io.filestream class...

Dim sz As Integer = 100

Dim sr As New IO.FileStream("Path", IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.None, sz, IO.FileOptions.RandomAccess)

Dim Buffer(sz) As Byte

Dim Offset As Integer = 0

sr.Read(Buffer, Offset, sz)

DMan1 at 2007-9-5 >

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# 2

So how do I tell it to read up to a certain string of characters?

nbrege at 2007-9-5 >

# 3

The example I gave above would read the first 100 bytes...then you could do

Array.Clear(Buffer, 0, Buffer.Length)

sr.Read(Buffer, 100, 2)

to read the next 2 bytes

DMan1 at 2007-9-5 >

# 4

But I need a way to check the characters as they're being read in. The character string that I'm seeking could be anywhere in the file, not just at the 100th byte. So how do I accomplish that?

nbrege at 2007-9-5 >

# 5

Take some time and read up on the filestream class it has methods that allow you to access a file any way you need to... even byte by byte...which sounds like what you need to do while keeping track of the number of bytes read....give it a shot ...write some code and then come back and post the code you are having problems with

public override int ReadByte()

Member of System.IO.FileStream

Summary:

Reads a byte from the file and advances the read position one byte.

Return Values:

The byte cast to an int, or -1 if reading from the end of the stream.

Exceptions:

System.ObjectDisposedException: The current stream is closed.

System.NotSupportedException: The current stream does not support reading.

DMan1 at 2007-9-5 >

# 6

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles Button1.Click

' Set # of display characters here

Dim CharBytesAfterFindToShow As Integer = 4

Dim result As String = ""

Dim place As Integer = 0

' Plug in the binary file here

Dim buffer() As Byte = System.IO.File.ReadAllBytes("c:\goodoval.jpg")

' Yes, there are random strings like 'NERK'

' embedded in some large binary files, but

' probably not any of yours.

' Plug in the search string here

Dim searchstr As String = "NERK"

'Load the search string into a byte array

Dim look3(searchstr.Length - 1) As Byte

For x As Integer = 0 To searchstr.Length - 1

look3(x) = CByte(Microsoft.VisualBasic.Asc(searchstr(x)))

' Search

Do While place <> -1

place = Array.IndexOf(buffer, look3(0), place, buffer.Length - place - 1)

If place = -1 Then

Exit Do

End If

Try

For x As Integer = 1 To searchstr.Length - 1

If Array.IndexOf(buffer, look3(x), place + x, 1) <> -1 Then

Else

place += 1

Exit Try

End If

MsgBox("match found at position " & place.ToString)

While place + searchstr.Length < buffer.Length

result += Chr(buffer(place + searchstr.Length))

place += 1

If result.Length = CharBytesAfterFindToShow Then

Exit While

End If

End While

If result = "" Or result = vbCrLf Then

result = "No characters after match"

End If

Exit Do

Catch ex As Exception

Exit Do

End Try

If place >= buffer.Length - 1 - searchstr.Length Then

Exit Do

End If

Loop

MsgBox(result)

End Sub

End Class

TallDude at 2007-9-5 >

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