FileStream/StreamWriter Problem

Hi All

I have a problem using FileStream and StreamWriter object.

I am creating file handle with CreateFile (Win32API) function and
passing to FileStream Constructor as an IntPtr

but the code creates only file xyz.txt , not write anything into it.


Please tell me what is wrong in code

Code:

---


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim fh As Integer
        Dim SW As StreamWriter
        Dim FS As FileStream
        fh = Win32API.CreateFile("C:\xyz.txt", Win32API.GENERIC_WRITE, 0, 0, Win32API.CREATE_ALWAYS, 0, 0)
        FS = New FileStream(fh, FileAccess.Write)
        FS.Flush()
        SW = New StreamWriter(FS)
        SW.WriteLine("Simple Text")
        FS.Flush()
        SW.Close()
        FS.Close()
        Win32API.CloseHandle(fh)
    End Sub

---

Win32API Class Code

Code:

---

Public Class Win32API
    Public Const GENERIC_WRITE = &H40000000
    Public Const CREATE_ALWAYS = 2
    Public Const OPEN_EXISTING = 3
    Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Integer, ByVal dwShareMode As Integer, ByVal lpSecurityAttributes As Integer, ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer, ByVal hTemplateFile As Integer) As Integer
    Public Declare Function CloseHandle Lib "kernel32" Alias "CloseHandle" (ByVal hObject As Long) As Long
End Class

---

Why are you using the API to create the file instead of using the FileStream to create it?

VB Code:

Dim fs As New FileStream("C:\xyz.txt", FileMode.Create)
        Dim sw As New StreamWriter(fs)
        sw.WriteLine("Simple Text")
        sw.Close()
        'closing the streamwriter will close the file but
        'you can still close on the filestream if you want
        fs.Close()

There are also these FileModes:
OpenOrCreate and CreateNew

you could do it like this also , just shortned down slightly :

VB Code:

Dim sWrite As IO.StreamWriter = New IO.StreamWriter(New IO.FileStream("C:\im_a_text.txt", IO.FileMode.OpenOrCreate))
            sWrite.Write("some text")
            sWrite.Close()

or if you just wish to create a file of any type , eg: txt you can also do this :

VB Code:

Dim f As IO.File
            f.Create("C:\im_a_text.txt")'/// create a new text file.

Thanks for your response.

Basicaly I want to send this "Simple Text" to devices like (LPT1: or
COM1:) This type of printing I want to use with Dot Matrix Printer. It Bypass Windows Printe Manager and print fasts simple text.
(The concept I am using in VB6 to print my clients Invoice)

When I use "LPT1:" or "COM1:" to as a parameter instead of file name VB.Net gives me following message when using it like this

Dim fs As New FileStream("LPT1:", FileMode.Open)


Error Message:

Quote:

---

An unhandled exception of type
'System.NotSupportedException occured in mscorlib.dll

Additional information: FileStream was asked to open a device
that take a string will only work with devices that are really files.
If you need support for devices like "com1:" or "lpt1:" then
call CreateFile yourself then use the FileStream constructors that
take an OS handle as an IntPtr.

---

The message shows It is possible.

Thanks again and hope for the solution.

One updation please

I found the reason why it is not writing.

Code:

---

FS = New FileStream(fh, FileAccess.Write)

---

In above code fh has a file handle, say it is 3776. Now the code is accepting it as file name not as file handle. It writes "Some Text" in 3776 file in project's bin directory

Now the QUESTTION is why not the above code handling fh as file handle instead of string ?

Please tell

Thanks

:rolleyes:

Try using an IntPtr type instead of Integer.

Thanks Edneeis


It is working fine and with also "LPT1:"

Thanks again.

This method might be what I'm looking for.
Anybody try it with a ps/pdf/print file?

Or would it just print the code within the file as text?

hmmmm.
-Lou

VB Code:

Dim fh As Integer
        Dim SW As StreamWriter
        Dim FS As FileStream
        fh = Win32API.CreateFile("C:\xyz.txt", Win32API.GENERIC_WRITE, 0, 0, Win32API.CREATE_ALWAYS, 0, 0)
        FS = New FileStream(fh, FileAccess.Write)
        FS.Flush()
        SW = New StreamWriter(FS)
        SW.WriteLine("Simple Text")
        FS.Flush()
        SW.Close()
        FS.Close()
        Win32API.CloseHandle(fh)

With this code posted by Parminder, I get the same problem - prints "Simple Text" to a file with the name of the file handle in the app's bin directory AND creates a blank file "C:\xyz.txt".

If I pass "LPT1:" as the first arg to CreateFile, I just get the file in the bin directory but no output to the printer at LPT1.

It won't allow IntPtr as the return type of CreateFile even with Option Strict Off.

I managed to resolve this as follows:

Call WriteToPort("LPT1:", "The text that i want to output to LPT1 port")

The

VB Code:

Public Class Win32API
 
        Public Const GENERIC_WRITE = &H40000000
        Public Const CREATE_ALWAYS = 2
        Public Const OPEN_EXISTING = 3
 
        Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" _
        (ByVal lpFileName As String, ByVal dwDesiredAccess As Integer, _
        ByVal dwShareMode As Integer, ByVal lpSecurityAttributes As Integer, _
        ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer, _
        ByVal hTemplateFile As Integer) As Integer
 
        Public Declare Function CloseHandle Lib "kernel32" Alias "CloseHandle" _
        (ByVal hObject As Long) As Long
 
    End Class
 
    Public Sub WriteToPort(ByRef sPort As String, ByRef sText As String)
 
        Dim FileHandle As Long
        Dim FileHandleIntPtr As IntPtr
        Dim FStream As FileStream
        Dim SWriter As StreamWriter
 
        FileHandle = Win32API.CreateFile(sPort, Win32API.GENERIC_WRITE, 0, 0, Win32API.CREATE_ALWAYS, 0, 0)
 
        FileHandleIntPtr = New IntPtr(FileHandle)
 
        FStream = New FileStream(FileHandleIntPtr, FileAccess.Write, False)
 
        FStream.Flush()
 
        SWriter = New StreamWriter(FStream)
 
        SWriter.WriteLine(sText)
 
        FStream.Flush()
 
        SWriter.Close()
 
        FStream.Close()
 
        Win32API.CloseHandle(FileHandle)
 
    End Sub

dear robertx

use api declaration like this (only)

Code:

---

    Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Integer, ByVal dwShareMode As Integer, ByVal lpSecurityAttributes As Integer, ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer, ByVal hTemplateFile As Integer) As IntPtr

---

all the best