How to convert fread to vb.net

You still need the class System.IO.StreamReader. You can rethink the whole I/O to get better performance but one way to improve it can be this: read the whole file at once into memory through System.IO.StreamReader.ReadToEnd and operate with the read data thereafter. Of course, if the volumes of your data allow…

[EDIT]
You operate too big volumes, in this case you need different approaches.
Let me see…

—SA

Use BinaryReader[^], it has the BinaryReader.ReadInt16[^] method.

Use a FileStream and since you don't care about the first 32768 bytes set Position to 32768 before passing it to the BinaryReader constructor.

The performance should be excellent ...

Whatever you are doing here is fairly expensive since you are repeatedly converting r,b,c to text

Trace.WriteLine("brc" & "," & b & "," & r & "," & c & "'" & iter)                   
XPositionOut.Clear()                   
XPositionOut.AppendText(c)                   
YPositionOut.Clear()                   
YPositionOut.AppendText(r)                   
BandPositionOut.Clear()                   
BandPositionOut.AppendText(b)                   
CellValueOut.AppendText(Convert.ToString(array3D(c, r, b)))

just declare three integers r, b and c - there seems to be no reason in your vb code for all the other stuff since the final destination for the data seems to be CellValueOut, and friends, inside the inner loop.

>> with more than a weeks worth of help from Microsoft technical support
I sincerely hope you don't have to pay for this

Regards
Espen Harlinn

Hi all - thanks for all the help - I seem to have this mostly working and the speed is acceptable.

Here is the working code

Public Sub LoadCubeData()
Dim d1 As DateTime = DateTime.Now
Dim MaxRows As Integer = 640
Dim MaxColumns As Integer = 640
Dim MaxPixels As Integer = 640
Dim MaxBands As Integer = 120
Dim r As Integer = 0
Dim b As Integer = 0
Dim c As Integer = 0
Dim p As Integer = 0
Dim Length As Long
Dim OutputfileNumber As Integer = 2
Dim OutputFileName As String
Dim DataLine As String

OutputFileName = Replace(InputImageName, ".cube", "_Band15.csv")
Try
FileOpen(OutputfileNumber, OutputFileName, OpenMode.Output, OpenAccess.Write)
Catch ex As Exception
MsgBox("output File open error " & vbCrLf & ex.Message)
Stop
End Try

'One complete pixel is 120 positions x 2 bytes = 240 bytes
Dim Completepixel As Integer = 240
'One complete row is 640 pixels = 640 * 240 = 153600
Dim CompleteRow As Integer = 153600
' One image is 640 complete rows = 640 * 156300
Dim i As Long = 0
Dim offset As Int64 = 32768 ' should offset be + 1 more ?
Dim Header As String = ""
Dim HeaderString As String = ""
Dim StartofFile As Int64 = 0
' Create the memory-mapped file.
Using mmf = MemoryMappedFile.CreateFromFile(InputImageName, FileMode.Open, "IMGAA", 500000000, MemoryMappedFileAccess.ReadWrite)
Using accessor = mmf.CreateViewAccessor(StartofFile, Length) ' since the length is set to 0, entire file is mapped
Dim ReadValue As Byte
Dim ByteArray(20) As Byte
For x = 0 To 13
ReadValue = accessor.ReadByte(x)
Header = ReadValue.ToString
ByteArray(x) = ReadValue
Next
HeaderString = System.Text.Encoding.Default.GetString(ByteArray)
MsgBox(HeaderString)
DataLine = HeaderString
PrintLine(OutputfileNumber, DataLine)
' suppose we need to find 15band for all the rows and columns
Dim band As Integer = 15
Dim band_value As UShort = 0
For r = 0 To MaxRows - 1
'For c = 0 To MaxColumns
For p = 0 To MaxPixels - 1
i = offset + r * CompleteRow + p * Completepixel + band
Try
accessor.Read(i, band_value) ' 15th value is read, compare if this needed
DataLine = "Band 15 Value at r=, " & r.ToString & ", p= ," & p.ToString & ", i= ," & i.ToString & ", Value = ," & band_value.ToString & ","
' MsgBox(DataLine)
PrintLine(OutputfileNumber, DataLine)
Catch
MsgBox("Exiting at Catch, i = " & i.ToString)
Exit For
End Try
Next
Next
End Using
End Using
FileClose(OutputfileNumber)
Dim d2 As DateTime = DateTime.Now
Dim diff1 As System.TimeSpan
'Console.WriteLine("d2({0})", d2)
diff1 = d2.Subtract(d1)
Trace.WriteLine("diff1 ")
Trace.WriteLine(diff1)

End Sub