Converting a byte() array to a double in VB.Net

Hi, I have this situation. I have a real stored in a varbinary field in a sql 2005 database. As I can't convert a varbinary to a real in sql 2005, I'm trying to do that in vb.net.

That field gets stored as a byte() array in a DataTable.

Now I would like to read that byte() into a double, or decimal variable. But I don't have much of a clue on how to do that...

From stackoverflow

• How is it stored in the varbinary field? String representation or actual binary representation?

• It really depends on how it's stored, but BitConverter.ToDouble may be your friend. That's assuming it's in IEE754 format. Where are you getting the data from in the first place?

• I don't know VB.net well, but know the .NET libraries.

  Wrap the byte[] in a MemoryStream and wrap that in a BinaryReader. Then use the BinaryReader.ReadDouble() method. See here and here for MSDN pages.

  Edit in response to this

  You are looking for a piece of code looking like this:

  //declare a test array
  Dim testArray As Byte() = {0, 0, 0, 0}
  //wrap it into a memory stream
  Dim memStream As MemoryStream = new MemoryStream(testArray)
  //wrap the stream in a binary reader
  Dim bReader As BinaryReader = new BinaryReader(memStream)
  //read a 32bit integer from the stream using the reader
  Dim count As Integer = bReader.ReadInt32();
  

• Jon Skeet, it doesn't work...

  biozinc, I'm trying to do as you say but I'm getting a "Unable to read beyond the end of the stream" exception.

  This is my code:

  Dim con As SqlConnection = New SqlConnection("Server=OMNILOGADMIN-PC;Database=master;Trusted_Connection=True;")
  Dim cmd As SqlCommand = New SqlCommand()
  Dim da As SqlDataAdapter = New SqlDataAdapter()
  Dim dt As DataTable = New DataTable()
  Dim ba As Byte()
  Dim val As Decimal
  Dim memStream As MemoryStream = New MemoryStream()
  Dim bReader As BinaryReader
  
  cmd.CommandText = "select convert(varbinary(max), cast(500 as real)) val"
  cmd.Connection = con
  
  da.SelectCommand = cmd
  
  Try
      con.Open()
      da.Fill(dt)
      ba = dt.Rows(0).Item(0)
      'val = BitConverter.ToDouble(ba, 0)
      memStream.Write(ba, 0, ba.Length)
  
      MessageBox.Show( _
       memStream.Capacity.ToString() & vbCrLf & _
       memStream.Length.ToString() & vbCrLf & _
       memStream.Position.ToString())
  
      bReader = New BinaryReader(memStream)
      memStream.Seek(0, SeekOrigin.Begin)
      Dim testArray As Byte() = {0, 0, 0, 0}
      Dim count As Integer = bReader.Read(testArray, 0, 3)
  
      MessageBox.Show(count & " - " & bReader.ReadDecimal())
  
  Catch ex As Exception
      MessageBox.Show("Erro: " & vbCrLf & ex.Message)
  Finally
      con.Close()
  End Try
  

  Any clues/sugestions? thanks a lot!

  Jon Skeet : What's the size of ba? What happens when you try using ToDouble?

• Public Function GetDateFromBytes(ByRef value() As Byte, _
                                      ByRef startindex As Int32) As Date
      'create a aray of Ints
      Dim IntValues() As Int32 = {BitConverter.ToInt32(value, startindex), _
                                      BitConverter.ToInt32(value, (startindex + 7)), _
                                      BitConverter.ToInt32(value, startindex + 15), _
                                       BitConverter.ToInt32(value, startindex + 31)}
  
      Return Date.FromBinary(New Decimal(IntValues))
  
  End Function