Copy the file into small pieces

Question

I want to copy the file into small pieces (to cancel the copy operation, if necessary).

I am trying to execute an unlabeled solution here: How to copy a file with the ability to undo a copy?

But I get a file with 0 bytes

What am I doing wrong?

Public Class Form1 Dim cancelled As Boolean = Nothing Dim input = New System.IO.FileStream("C:\1.txt", System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read) Dim output = New System.IO.FileStream("C:\Nueva carpeta\1.txt", System.IO.FileMode.CreateNew, System.IO.FileAccess.Write, System.IO.FileShare.Write) Public Sub CopyStream(ByVal inputStream As System.IO.Stream, ByVal outputStream As System.IO.Stream) 'Dim buffer = System.IO.File.ReadAllBytes("C:\1.txt") Dim buffer = New Byte((1024) - 1) {} Dim bytesRead As Integer = 1 While (inputStream.Read(buffer, 0, buffer.Length) > 0) outputStream.Write(buffer, 0, bytesRead) 'bytesRead += 1 If cancelled Then MsgBox("operacion cancelada") Return End If End While inputStream.Close() outputStream.Close() MsgBox("operacion terminada") End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click CopyStream(input, output) End Sub End Class 

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UPDATE 1:

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I tried to follow the Virtlink response steps and put the missing parts in my source code, but I still get a null byte.

 > Public Class Form1 Dim input = New System.IO.FileStream("C:\Test.txt", System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read) Dim output = New System.IO.FileStream("C:\Test_New.txt", System.IO.FileMode.CreateNew, System.IO.FileAccess.Write, System.IO.FileShare.Write) Public Sub CopyStream(ByVal inputStream As System.IO.Stream, ByVal outputStream As System.IO.Stream) Dim buffer = New Byte(1024) {} Dim bytesRead As Integer ' Read some bytes While (bytesRead = inputStream.Read(buffer, 0, buffer.Length) > 0) ' Write them to the output outputStream.Write(buffer, 0, bytesRead) End While End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click CopyStream(input, output) End Sub End Class 

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UPDATE 2:

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MY LAST FAILURE AGAINST:

  Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim input_filepath As String = "C:\Test.txt", output_filepath As String = "C:\Test_New.txt" Dim input = New System.IO.FileStream(input_filepath, System.IO.FileMode.Open, System.IO.FileAccess.ReadWrite) Dim output = New System.IO.FileStream(output_filepath, System.IO.FileMode.Create, System.IO.FileAccess.ReadWrite) CopyStream(input, output) ' For Testing: If New IO.FileInfo(output_filepath).Length = 0 Then IO.File.Delete(output_filepath) : Application.Exit() Else Process.Start("Notepad", output_filepath) End Sub Public Sub CopyStream(ByVal inputStream As System.IO.Stream, ByVal outputStream As System.IO.Stream) Dim buffer = New Byte(1024) {}, bytesRead As Integer While ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0) outputStream.Write(buffer, 0, bytesRead) End While inputStream.Flush() : outputStream.Flush() inputStream.Close() : outputStream.Close() End Sub End Class 

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UPDATE 3:

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DECISION

The problem was in VB.NET. I cannot assign a value to a variable in a loop condition, so this is a working Sub:

  Public Sub CopyStream(ByVal inputStream As Stream, ByVal outputStream As Stream) Dim buffer = New Byte(1025) {} Dim bytesRead As Integer = 0 Do bytesRead = inputStream.Read(buffer, 0, buffer.Length) If bytesRead > 0 Then outputStream.Write(buffer, 0, bytesRead) End If Loop While (bytesRead > 0) outputStream.Flush() inputStream.Close() : outputStream.Close() End Sub 

Answer 1

You need to understand what you are doing and how it works.

First you allocate a buffer.

 Dim buffer = New Byte(1024) {} 

Then you go over and read some data from the input stream. Data is placed in buffer , starting from 0 , no more than buffer.Length bytes. The method returns the number of bytes that it actually read and buffered.

 bytesRead = inputStream.Read(buffer, 0, buffer.Length) 

If the number of bytes read is greater than 0, you have not reached the end of the file.

 While (bytesRead > 0) 

Then you write exactly those bytes that were read ( bytesRead bytes) into the output stream. Write bytes from buffer , start at index 0 and write bytesRead number of bytes.

 outputStream.Write(buffer, 0, bytesRead) 

Since the stream will buffer what you wrote for performance reasons, you will need to clear and close the output stream.

 outputStream.Flush() outputStream.Close() 

Combining this:

 Dim buffer = New Byte(1024) {} Dim bytesRead As Integer ' Read some bytes While ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0) ' Write them to the output outputStream.Write(buffer, 0, bytesRead) If cancelled Then MsgBox("operacion cancelada") Return End If ' Repeat End outputStream.Flush() outputStream.Close() 

_{The last time I wrote VB, over a decade ago. You must ensure that the syntax is correct.}

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Notice how the source code contains this line:

 While ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0) 

Do you see the bytesRead = part? You did not copy this into your code. It is important to keep the number of bytes read.

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Final code: this works on my computer:

 Imports System Imports System.IO Namespace ConsoleApplication1 Friend Class Program Private Shared Sub Main(args As String()) Program.CopyMyFiles() Console.WriteLine("DONE!") Console.ReadLine() End Sub Private Shared Sub CopyMyFiles() Dim input_filepath As String = "Test.txt" Dim output_filepath As String = "Test_New.txt" Dim input As FileStream = New FileStream(input_filepath, FileMode.Open, FileAccess.ReadWrite) Dim output As FileStream = New FileStream(output_filepath, FileMode.Create, FileAccess.ReadWrite) Program.CopyStream(input, output) End Sub Public Shared Sub CopyStream(inputStream As Stream, outputStream As Stream) Dim buffer As Byte() = New Byte(1025) Dim bytesRead As Integer bytesRead = inputStream.Read(buffer, 0, buffer.Length) While bytesRead > 0 outputStream.Write(buffer, 0, bytesRead) bytesRead = inputStream.Read(buffer, 0, buffer.Length) End While outputStream.Flush() inputStream.Close() outputStream.Close() End Sub End Class End Namespace