How to find exactly byte, then seek until there is null byte and write to a binary file.

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How to read exactly byte, then seek until there is null byte, and write the seeked byte to a binary file.

VB

    Public Function FindBytes(ByVal src As Byte(), ByVal find As Byte()) As Integer
        Dim index As Integer = -1
        Dim matchIndex As Integer = 0
        ' handle the complete source array
        For i As Integer = 0 To src.Length - 1
            If src(i) = find(matchIndex) Then
                If matchIndex = (find.Length - 1) Then
                    index = i - matchIndex
                    Exit For
                End If
                matchIndex += 1
            Else
                matchIndex = 0
            End If
        Next
        Return index
    End Function

    Private Function GetBytes(ByVal filename As String) As Byte()
        Dim fs As New IO.FileStream(filename, IO.FileMode.Open, IO.FileAccess.Read)
        ' Create a byte array of file stream length
        Dim ImageData As Byte() = New Byte(fs.Length - 1) {}
        'Read block of bytes from stream into the byte array
        fs.Read(ImageData, 0, System.Convert.ToInt64(fs.Length))
        'Close the File Stream
        fs.Close()
        'return the byte data
        Return ImageData
    End Function
	
	
Dim PNGStart As Byte() = {&H89, &H50, &H4E, &H47} ' PNG HEADER
Dim PNGEnd As Byte() = { &H49, &H45, &H4E, &H44, &HAE, &H42, &H60, &H82}

Dim StartPosition As Integer = FindBytes(GetBytes(filename), PNGStart)

SO How to Loop throw PNGStart to PNGEnd and write it to a file?

Note: I have found FindBytes function in other site, but I don't remember it's name, credits to the one who created it.

Posted 4-Feb-13 15:17pm

Leecherman

Updated 5-Feb-13 4:36am

Pete O'Hanlon

v3

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Comments

Sergey Alexandrovich Kryukov 4-Feb-13 21:26pm

What did you try so far? Why it's the problem?
—SA

Leecherman 4-Feb-13 22:05pm

I'm trying to read specie bytes from file, then after finding it, i will make the start position from the founded bytes, then seek and writing to binary file until null bytes is found.

tiggerc 5-Feb-13 10:01am

do you have some code?
I would suggest reading the bytes into an array, looping through the array building another list of bytes until the byte you are at is null( 00 ) then writing your built list to a file.

then continue the process until you have read all bytes and created all the files you want.

Have a go at it, we will help, but you need to at least show some of your code.

Leecherman 5-Feb-13 10:14am

No problem while getting bytes from file, but the problem is when finding the exact byte, and loop until there is null byte.

Leecherman 5-Feb-13 11:18am

thanks, but this doesn't accept {&H89, &H50, &H4E, &H47}
it only accept one byte!

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OriginalGriff · Answer 1 · 2013-02-05T05:11:00

This is a Brute-force-and-ingorance approach, but...try:

VB

Dim path As String = "D:\Temp\MyPic.jpg"
Dim startdata As Byte = &Hff
Dim enddata As Byte = &H0
Dim data As Byte() = File.ReadAllBytes(path)
Dim extract As Byte()
Dim startIndex As Integer
For startIndex = 0 To data.Length - 1
    If data(startIndex) = startdata Then
        Exit For
    End If
Next
startIndex += 1
Dim endIndex As Integer
For endIndex = startIndex To data.Length - 1
    If data(endIndex) = enddata Then
        Exit For
    End If
Next
extract = New Byte(endIndex - startIndex - 1) {}
Array.Copy(data, startIndex, extract, 0, endIndex - startIndex)