[Help] Search for data in binary file

[Fenryr]

Basically what i want to do is take a file, and be able to find 4 consecutive hexadecimal values (For example, 44 66 34 25) and have the program tell me where in the file that sequence appears. Any help would be appreciated, or tell me if i didn't explain the situation well enough. I want to be able to do this in VB 2008 or VB 6, preferably 2008.

[Fenryr]

Ok, i kinda figured out the answer to my question, but it could be very inefficient when working with bigger files. Basically i just have the program check to see if the current value is the target amount, and if it is not, then it adds one to the current value. Here's some code to explain:

        Dim fileContents As Byte()
        fileContents = My.Computer.FileSystem.ReadAllBytes("C:\Test.txt")
        Dim h As Integer = 0

        If fileContents(h) <> &HB5 And fileContents(h + 1) <> &HF6 Then
            Do Until fileContents(h) = &HB5 And fileContents(h + 1) = &HF6
                h = h + 1
            Loop

        End If
        If fileContents(h) = &HB5 And fileContents(h + 1) = &HF6 Then
            MsgBox("yay, success " & Hex(h))
        End If

It works, but barely and only for the first time the sequence appears in a file, and if it dosent appear at all, the program crashes from an overflow error. Can anyone give advice, or help me refine it?

[Apoc]

''' <summary>
''' Gets the offsets of a specified byte array in a file.
''' </summary>
''' <param name="file">The file to search in.</param>
''' <param name="bytes">The bytes to search for.</param>
''' <returns>A list containing the offsets for the byte pattern specified.</returns>
Public Shared Function GetOffsets(ByVal file As String, ByVal bytes As Byte()) As List(Of Long)
    Dim ret As New List(Of Long)()
    Using s As Stream = New FileStream(file, FileMode.Open)
        Using br As New BinaryReader(s)
            While True
                Try
                    ' Save the current position so we can add it
                    ' if this offset is the spot we want.
                    ' Also so we can go back to here, if it's not.
                    Dim pos As Long = br.BaseStream.Position
                    
                    ' Read in the same amount of bytes that we have
                    ' in the bytes param.
                    Dim ba As Byte() = br.ReadBytes(bytes.Length)
                    
                    Dim ok As Boolean = True
                    ' Small error check here.
                    If bytes.Length = ba.Length Then
                        For i As Integer = 0 To bytes.Length - 1
                            If ba(i) <> bytes(i) Then
                                ok = False
                                ' Jump out immediately.
                                ' It's not what we want, so there's no need to check more.
                                Exit For
                            End If
                        Next
                    End If
                    If ok Then
                        ' Add the position we got these 4 bytes from.
                        ret.Add(pos)
                    End If
                    ' Since the BinaryReader has jumped from pos to (pos + bytes.Length)
                    ' we need to go back to where we were, plus 1 offset to read again.
                    br.BaseStream.Position = pos + 1
                Catch generatedExceptionName As EndOfStreamException
                    ' End of file
                    Exit Try
                End Try
            End While
        End Using
    End Using
    Return ret
End Function

You can now just use

Public Sub test()
    Dim bytes As Byte() = New Byte() {44, 66, 34, 25}
    Dim offsets As List(Of Long) = GetOffsets("C:\MyFileToCheck.extension", bytes)
    ' Do whatever with the offsets here.
End Sub

Let me know if you have any issues.

Of course, you need to import the proper namespaces. (System.IO, and System.Collections.Generic, probably System as well.)

[Fenryr]

Thank you, it seems to work, but how can i now use the offsets, like if i wanted to view them?

EDIT: it's actually not working, when i use it, the form freezes, then goes white and the title bar says not responding. but it may just be because i'm not using it correctly.

[Apoc]

Large files can do that. (I suggest running the method in a separate thread.)

And using the offsets is up to you. Look at how I opened the BinaryReader object, and set the br.BaseStream.Position property to the offset. (Same idea applies.)

[Fenryr]

But i mean just using that code on a small 20kb text file where the sequence appears it still crashes. But i have made my own code based on what you gave me and it seems to work on small files, but with larger ones it just opens a message box with nothing in it, rather than the offsett.

I would put it in a code box but it's too wide at some parts






Dim h As Integer = &H0
Dim offset(255) As String
Function searchfile()

Dim fileContents As Byte()
fileContents = My.Computer.FileSystem.ReadAllBytes("C:\test.txt")



If fileContents(h) <> &H4B And fileContents(h + 1) <> &H4E And fileContents(h + 2) <> &H43 And fileContents(h + 3) <> &H4D Then
Do Until fileContents(h) = &H4B And fileContents(h + 1) = &H4E And fileContents(h + 2) = &H43 And fileContents(h + 3) = &H4D
h = h + 1
Loop

End If

If fileContents(h) = &H4B And fileContents(h + 1) = &H4E And fileContents(h + 2) = &H43 And fileContents(h + 3) = &H4D Then

offset(0) = Hex(h)
End If


End Function





then to use:

    

  searchfile()

        MsgBox(offset(0))

its a little messy but it seems to work very well on small files( finds 4b 4e 43 4d in a file)