In the following subroutine, will the StreamReader be closed properly when the exception is thrown? Or do I have do something myself to ensure this?
Sub mySub()
Dim sr As StreamReader = File.OpenText("someFilename")
Dim line As String = sr.ReadLine()
While Not (line Is Nothing)
' Some logic here
If someCondition Then
Throw New Exception("someExplanation")
End If
line = sr.ReadLine()
End While
End Sub
You should wrap the StreamReader variable in a using statement.
Using sr as StreamReader = File.OpenText("someFilename")
...
End Using
Stream won't be closed until the process is terminated. Even it does you should close it. Best way is to use "using" method as it mentioned before. But it doesn't cause data loss unlike while writing it does. In other translation, you should close the Stream, but it's not critic.
Related
I get the feeling this is something really simple, but I've tried I don't know how many permutations of vbNewLine, Environment.NewLine, sMessage & vbNewLine (or Environment.Newline) I've tried, or how many pages on this site, or through Google I've looked at but nothing has worked.
I even tried getting help from a VB.Net discord channel I'm a part of and they suggested to do the same things that I've done and the procedure is still writing each new log entry at the end of the previous one in a continuous string. My writer is below. Am I missing something simple?
Edit: The code that worked is below in case anyone else comes along with the same issue. If you want to see the original code it's in the edit log.
Option Explicit On
Imports System.IO
Public Class WriteroLog
Public Shared Sub LogPrint(sMessage As String)
Dim AppPath As String = My.Application.Info.DirectoryPath
If File.Exists($"{AppPath}\Log.txt") = True Then
Try
Using objWriter As StreamWriter = File.AppendText($"{AppPath}\Log.Txt")
objWriter.WriteLine($"{Format(Now, "dd-MMM-yyyy HH:mm:ss")} – {sMessage}")
objWriter.Close()
End Using
Catch ex As Exception
MsgBox(ex)
Return
End Try
Else
Try
Using objWriter As StreamWriter = File.CreateText($"{AppPath}\Log.Txt")
objWriter.WriteLine($"{Format(Now, "dd-MMM-yyyy HH:mm:ss")} – {sMessage}")
objWriter.Close()
End Using
Catch ex As Exception
MsgBox(ex)
Return
End Try
End If
End Sub
End Class
The File.AppendText() method creates a new StreamWriter that is then used to append Text to the specified File.
Note, reading the Docs about this method, that you don't need to verify whether the File already exists: if it doesn't, the File is automatically created.
As a side note, when creating a Path, it's a good thing to use the Path.Combine method: it can prevent errors in the path definition and handles platform-specific formats.
Your code could be simplified as follows:
Public Shared Sub LogPrint(sMessage As String)
Dim filePath As String = Path.Combine(Application.StartupPath, "Log.Txt")
Try
Using writer As StreamWriter = File.AppendText(filePath)
writer.WriteLine($"{Date.Now.ToString("dd-MMM-yyyy HH:mm:ss")} – {sMessage}")
End Using
Catch ex As IOException
MsgBox(ex)
End Try
End Sub
The File.CreateText does not assign result to "objWrite", should be:
objWriter = File.CreateText($"{AppPath}\Log.Txt")
Not really sure if this is the root of your problem, but it is an issue.
In essences, your logic is re-opening or creating the stream "objWriter" for every call to this method. I would recommend you initialize "objWriter" to Nothing and only define if it is Nothing.
Set to Nothing as below.
Shared objWriter As IO.StreamWriter = Nothing
Then add check for Nothing in logic.
Please take a look at this code. For some reason that I can't figure out, the File.Delete() line isn't getting fired and I'm not getting an error.
' hard-coded for testing
Dim path As String = "C:\Program Files (x86)\Test\Program\Program.exe"
Dim appDir As String = My.Application.Info.DirectoryPath
Dim iniPath As String = appDir & "\config.ini"
Dim outputPath As String = appDir & "\output.ini"
Dim textLine As String = ""
Dim reader = File.OpenText(iniPath)
Dim writer = New StreamWriter(outputPath)
' Read the lines in the ini file until the pathToExecutable line is found and write the path to that line
While (InlineAssignHelper(textLine, reader.ReadLine())) IsNot Nothing
If textLine.StartsWith("pathToExecutable=") Then
writer.WriteLine("pathToExecutable=" & path)
Else
writer.WriteLine(textLine)
End If
End While
reader.Dispose()
reader.Close()
writer.Dispose()
writer.Close()
File.Copy(outputPath, iniPath, True)
File.Delete(outputPath) ' THIS ISN'T GETTING FIRED
Return path
You stated that you are not getting an error, but if you don't implement exception handling, you're most probably getting errors and throwing them away (pun intended).
Use a try/catch around any of your System.IO.File operations, and even more, you can implement specific handles and catch specific exceptions.
Try
File.Copy(outputPath, iniPath, True)
File.Delete(outputPath) ' THIS ISN'T GETTING FIRED
Catch ioException As IOException
'The specified file is in use.
MessageBox.Show(ioException.Message)
Catch ex As Exception
'Some other error apart for file in use.
MessageBox.Show(ex.Message)
End Try
Ericosg's suggestion about using a try/catch lead me to the issue: I had the file open in a streamreader earlier in my code, but never closed it there.
three questions please
1) If there is an exception in the try below will the request stream automatically close as it is in a using
2)do I even need the requestStream.Close() and requestStream.Dispose() as it is in a using?
3) do I need to close the System.Net.FtpWebRequest?
Try
Dim rqst As System.Net.FtpWebRequest = DirectCast(System.Net.WebRequest.Create("ftp://1.com/text.txt"), System.Net.FtpWebRequest)
rqst.Credentials = New System.Net.NetworkCredential("useb", "pass")
rqst.Method = System.Net.WebRequestMethods.Ftp.UploadFile
'Throw New ApplicationException("Exception Occured")
Dim fle() As Byte = System.IO.File.ReadAllBytes("C:\test.txt")
Using requestStream As Stream = rqst.GetRequestStream()
requestStream.Write(fle, 0, fle.Length)
requestStream.Close() 'do I need this?
requestStream.Dispose() 'do I need this ?
End Using
Catch ex As Exception
MessageBox.Show(ex.Message.ToString())
End Try
No you dont need if you are using using. As using itself is used to dispose of. Also the reason for the "using" statement is to ensure that the object is always disposed correctly, and it doesn't require explicit code to ensure that this happens.
Dispose method is called immediately when control flow exits the using block.
Yes. If the exception occurs while executing code inside the using statement, the stream will be disposed before it goes to the Catch block.
Consider the code:
On Error Goto ErrorHandler
Using sr As StreamReader = New StreamReader(OpenFile)
str = sr.ReadToEnd
sr.Close()
End Using
Exit Sub
ErrorHandler:
If there is an error inside the Using block how do you clean up the sr object?
The sr object is not in scope in ErrHandler so sr.Close() cannot be called. Does the Using block cleanup any resources automatically even if there is an error?
As codeka says, you don't need to call Close on sr. It'll called automatically, and that includes if there is an error. Using the using statement gives you the same functionality as try ... finally ... end try.
And as you see in the answers to your other question, you shouldn't be using On Error etc just do:
Try
Using sr as StreamReader ...
...
End Using
Catch ex as SomeException
...
End Try
Yes, the using block will automatically call IDisposable.Dispose (which, for a StreamReader is the same as calling Close) so there's nothing you need to do (that's the whole point of using blocks!)
This code:
Using sr As StreamReader = New StreamReader(OpenFile)
str = sr.ReadToEnd
sr.Close()
End Using
Is really equivalent to this:
Dim sr As StreamReader = Nothing
Try
sr = New StreamReader(OpenFile)
sr.Close() ' notice: unnecessary '
Finally
sr.Close()
End Try
Keep in mind that code within a Finally block will always execute before the method returns (if it throws an exception of its own, well, then you're in for a world of hurt). So the sr.Close line you have within your Using block is superfluous (notice it is unnecessary in the equivalent code using Try/Finally since sr.Close will be called in the Finally no matter what -- exception thrown or not).
(VB.NET, .NET 3.5)
I wrote the following function to read some text from txt file. It was working fine but now it's not. It keeps giving me this error message
"IOException was unhandled" and
" The process cannot access the file 'F:\kh_matt\ch1.txt' because it is being used by another process."
The ch1.txt is not even opened or being used by any program at all. I tried to move ch1.txt to another location (Drive D) still I got the same message error but just different location it says The process cannot access the file 'D:\ch1.txt' because it is being used by another process."
Here's my code block :
Private Sub btnRead_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRead.Click
Dim reader As StreamReader
Dim filelocation As String
filelocation = "F:\kh_matt\ch1.txt"
Dim chid As Integer
chid = 1
If System.IO.File.Exists(filelocation) = True Then
reader = New StreamReader(New FileStream(filelocation, FileMode.Open))
Else
MsgBox(filelocation, MsgBoxStyle.OkOnly)
End If
Dim MyStream As New StreamReader(Path.Combine(Application.StartupPath, filelocation))
Dim vArray() As String = MyStream.ReadToEnd.Split(CChar("$"))
MyStream.Close()
Dim count As Integer
For d As Integer = 0 To vArray.Length - 1 Step 1
If d = vArray.Length - 1 Then
Exit For
End If
InsertKh(chid, d + 1, vArray(d))
count = d + 1
Next
MsgBox("Done Inserting")
End Sub
It always points to this code :
Dim MyStream As New StreamReader(Path.Combine(Application.StartupPath, filelocation))
Where I debug and press the respective button. Can anyone point out what the problem is ? Thanks
I think this is your problem:
If System.IO.File.Exists(filelocation) = True Then
reader = New StreamReader(New FileStream(filelocation, FileMode.Open))
If the file exists it will open a StreamReader on it, then try and open another StreamReader on the same file, which will lock the file, causing this line:
Dim MyStream As New StreamReader(Path.Combine(Application.StartupPath, filelocation))
to fail.
Also, some pointers:
consider using the System.IO.File.ReadAllText() method instead, much easier
if you must use streams, wrap them in a using block to ensure they're freed correctly, for example:
`
Dim vArray() As String
using (Dim MyStream As New StreamReader(Path.Combine(Application.StartupPath, filelocation))
{
vArray = MyStream.ReadToEnd.Split(CChar("$"))
}
(sorry if the above code isn't 100% correct, I don't write much VB.Net)
It seems you open the file twice, which is probably what's causing your error:
reader = New StreamReader(New FileStream(filelocation, FileMode.Open))
...
Dim MyStream As New StreamReader(Path.Combine(Application.StartupPath, filelocation))
Are you sure that's what you intend to do? It looks like you can remove MyStream and use reader instead. Also, you don't have to use Path.Combine, since filelocation is not relative.
Make sure that you close your stream & streamreader once you've finished reading the file, even when an exception is being thrown.
Use a try/finally block, and close the stream / streamreader in the finally block.
Thanks all for the reply. It's my mistake. I forgot to comment out my code that I wrote for testing earlier. After commenting this code out it works like before.
'If System.IO.File.Exists(filelocation) = True Then
' reader = New StreamReader(New FileStream(filelocation, FileMode.Open))
'Else
' MsgBox(filelocation, MsgBoxStyle.OkOnly)
'End If
Have a good day.