[VB.NET 2008] Insert binary data into file

[Patrickh0]

Hi, I'm trying to insert varying amounts of bytes into a file at a certain offset, but I'm a little lost. I'm assuming there would be some sort of shift and add, but I'm unsure on a proper method. Any help would be appreciated.

Note: I don't want to overwrite any data, just insert a specified number of bytes.

[jmcilhinney]

You can create a FileStream and call the Seek method to move the file pointer to a specific position. That said, I don't it's possible to insert data into a file like that. I think it would require reading the existing contents, then writing the contents out again in two parts, with the new data written in between.

[pvbangera]

Dim FH As Integer
        FH = FreeFile()
        FileOpen(FH, "MyFile.abc", OpenMode.Binary, OpenAccess.ReadWrite)

You need to build your own logic for getting the offset based on your file type.

[Patrickh0]

Thanks for the responses. I sort of got what I wanted by doing this:

Public Sub Insert(ByVal StartOffset As Int32, ByVal Size As Int32)
        Dim br As New IO.BinaryReader(New IO.FileStream(MAP.Path, IO.FileMode.Open, IO.FileAccess.Read))
        Dim block As Byte()
        Dim bytesleft As Integer = br.BaseStream.Length - StartOffset
        br.BaseStream.Position = StartOffset
        block = br.ReadBytes(bytesleft)
        br.Close()
        Dim bw As New IO.BinaryWriter(New IO.FileStream(MAP.Path, IO.FileMode.Open, IO.FileAccess.Write))
        Dim zero As Byte = 0
        For i As Integer = 0 To Size - 1
            bw.BaseStream.Position = StartOffset + i
            bw.Write(zero)
        Next
        bw.BaseStream.Position = StartOffset + Size
        bw.Write(block)
        bw.Close()
    End Sub

Is there a smarter/faster way of doing this? This code is pretty sluggish... Thanks in advance.

[jmcilhinney]

You could open the file once only for read/write access.