It is a very basic code that I'm using for my college coursework. Unfortunately, we're only allowed to use StreamRead and StreamWrite type functions for marking reasons. I'm unsure as to how to basically rewrite the line already in the file with a new value. I know I could delete the file and recreate but we also get marked down for that sort of thing. Any ideas?
Private Function WriteTaxableIncome()
Dim TaxableIncomeStreamWriter As IO.StreamWriter
TaxableIncomeStreamWriter = New IO.StreamWriter("C:\Computing\Coursework\TaxableIncome.txt", True)
TaxableIncomeStreamWriter.WriteLine(TaxableIncome)
TaxableIncomeStreamWriter.Close()
End Function
When you create the StreamWriter instance, you have called the constructor with New (path As String, append As Boolean), and passed True into the append argument, so that will make the writer append to the file, instead of overwrite it. Seems like the exact opposite of what you want to do. Instead, pass False. Also, use a Using block which will Open and Close the writer. It automatically calls Dispose so you can be sure no part of it is left open.
Using writer As New IO.StreamWriter("C:\Computing\Coursework\TaxableIncome.txt", False)
writer.WriteLine(TaxableIncome)
End Using
Related
I am writing a program that writes data to a text file at different points in my code, for example in different subroutines, functions or at different parts of subroutines (being scattered around).
First, I Dim the file writer:
Dim CurrentHisWriter As System.IO.StreamWriter
I tell it where to write to:
CurrentHisWriter = New System.IO.StreamWriter("C:\ProgramData\Japanese Conjugation Helper\LastSearch.txt")
Then, I actually write things:
CurrentHisWriter.Writeline("thing to write")
The problem is that I have to change to a different subroutine and then keep on writing to a file, so I have to close the writer and then dim another one in another subroutine:
CurrentHisWriter.Close
NewSubroutine()
[NewSubroutine]:
Dim CurrentHisWriter As System.IO.StreamWriter
CurrentHisWriter = New System.IO.StreamWriter("C:\ProgramData\Japanese Conjugation Helper\LastSearch.txt")
But then when I do this, I gives me one of a couple errors:
The program is has an instance of the file running
Some thing to do with there being no object (I don't remember exactly)
What is a reliable way programming the writing to files without having to worry about closing the writer at every point I change subroutines. I'm not sure about how objects and instances work and so the only thing I can do now is make a catch loop around every single line that uses the "CurrentHisWriter.Writeline" but this isn't really working too.
I know my lack of knowledge in this doesn't help explain, but I tried my best.
The naive approach would be like:
Sub Main()
MethodA()
MethodB()
End Sub
Sub MethodA()
Log("Starting method A")
End Sub
Sub MethodB()
Log("Starting method B")
End Sub
Sub Log(message as String)
System.IO.File.AppendAllText("C:\temp\my.log", message)
End Sub
File.AppendAllText is pretty good at closing things off so you can subsequently write to it elsewhere
A better approach would be to have a class whose job it is to build this file, and it builds it all into a stringbuilder and then writes it once. Multiple of your methods use that class, build that file... The class can either implement some timed/periodic dumping of data to disk (if it's like logging, never ending, thousands of events per second.. but then perhaps you'd just use a logging framework rather than reinvent the wheel), or it has a write method that saves the rendering of it to disk
If there is another specialized application of your data at work here, for example if you're generating XML or JSON you should look at specific serialization approaches for those (wheels that have already been invented)
I use
FileOpen(1, "file.txt", OpenMode.Append)
Now you can write from any other subroutine
PrintLine(1, "text to write")
Until the file is closed
FileClose(1)
But maybe you could solve your problem this way:
Define CurrentHisWriter outside of subroutine as
Private CurrentHisWriter As System.IO.StreamWriter = ....
Then you won't have to close and reopen the writer, all your Subs and functions will have access to it.
For my current project in need a way to use ä,ö etc. in a datatable that is written to a .csv
It is the same project as in: VB Reading data from SQL Server to Array, writing into .CSV
I know that I need UTF-8 but how do I use it ?
Unlike VB6/VBScript/VBA, VB.Net strings already use full Unicode internally. You can already put accented characters in your string variables (and string members for other objects), and you don't need to do anything special.
There are three things you do need to watch for, though.
First, you must be sure to use NVARCHAR rather than VARCHAR for your Sql Server columns, as well as your ADO.Net parameters. You may also need to be careful about what collation you have (but the default is almost certainly fine here).
Second, when you open your StreamWriter, you need to use unicode-capable correct Encoding. System.Text.UTF8Encoding is one option. You could also do System.Text.UnicodeEncoding (which is UTF16) or System.Text.UTF32Encoding and get accurate output.
Finally, just because you successfully create a unicode CSV file, this does not mean your downstream consumers will handle the file correctly. A lot of text editors and other tools like to assume csv data is ASCII. But that's really outside of your scope. All you can is give them valid data. If they don't process it, that's on them :)
So assuming the database is correct, and based on the other question, you have this code:
Sub WriteCsvFiles(destPath As String, headings As String(), dt As DataTable)
Dim separator As Char = ";"c
Dim header = String.Join(separator, headings)
For Each r As DataRow In dt.Rows
Dim destFile = Path.Combine(destPath, r(0).ToString().Trim() & ".csv")
Using sw As New StreamWriter(destFile)
sw.WriteLine(header)
sw.WriteLine(CsvLine(r.ItemArray, separator))
End Using
Next
End Sub
This is close. However, take a look at the remarks in the documentation for the StreamWriter constructor:
This constructor creates a StreamWriter with UTF-8 encoding without a Byte-Order Mark (BOM), so its GetPreamble method returns an empty byte array. The default UTF-8 encoding for this constructor throws an exception on invalid bytes. This behavior is different from the behavior provided by the encoding object in the Encoding.UTF8 property.
So we kind of already have UTF-8 data, but to really have a correct UTF-8 file, including correct byte-order handling for certain wide characters, we need to change things just a little bit. Where you have this right now:
Using sw As New StreamWriter(destFile)
should become:
Using sw As New StreamWriter(destFile, False, Encoding.UTF8)
It also seems very odd to create a separate file for every row that will all have the same structure. I know it's in your original question, but I'd really push back on that, or find out why, and the maybe re-write the method as so:
Sub WriteCsvFile(destFile As String, headings As IEnumerable(Of String), dt As DataTable)
Dim separator As Char = ";"c
Dim header As String = String.Join(separator, headings)
Using sw As New StreamWriter(destFile, False, Encoding.UTF8)
sw.WriteLine(header)
For Each r As DataRow In dt.Rows
sw.WriteLine(CsvLine(r.ItemArray, separator))
Next
End Using
End Sub
This is a very simple question.
I am trying to add items to the Inventory class list from a .txt file. However i can't use the word 'New' in this line otherwise it give a syntax error:
New Inventory("Rod", 1)
Function GetInventory() As IEnumerable(Of Inventory)
If System.IO.File.Exists(loc) = True Then
If System.IO.File.ReadAllText(loc).Count > 0 Then
Dim file As System.IO.StreamReader
file = My.Computer.FileSystem.OpenTextFileReader(loc)
Do While file.Peek() >= 0
New Inventory("Rod", 1)
Loop
Return New Inventory
file.Close()
End If
End If
End Function
How do I go about this???
Thank you.
With what you have, you're reading the entire file into memory twice. That's crazy wasteful.
Also, you don't need the .Exists() check here. The file system is volatile, meaning it's possible for the file to cease to be available between when you check .Exists() and when you try to access the file. A good program will still have a good exception handler for when the file does not exist, and now that you have an exception handler, the .Exists() check is just redundant. It's not saving you the performance hit you likely think it is. Also, this method is probably the wrong place to handle the exception. That's usually better to do in the calling code somewhere, meaning you can skip error checking here completely.
You can get this whole method down to a single statement that will cut your execution time in half:
Function GetInventory(ByVal loc As String) As IEnumerable(Of Inventory)
Return IO.File.ReadLines(loc).Select(Function(i) New Inventory(i, 1))
End Function
Either I'm missing something really obvious or something about vb is really messed up. I'm trying to read in from a file and add the lines to an arraylist... pretty simple If I add strings to the arraylist this way
selectOptions.Add("Standard")
selectOptions.Add("Priority")
selectOptions.Add("3-Day")
selectOptions.Add("Overnight")
I have no problems
But when I do this it appears to end up empty which makes no sense to me.
Dim reader As StreamReader = My.Computer.FileSystem.OpenTextFileReader(path)
Dim line As String
Do
line = reader.ReadLine
selectOptions.Add(line)
Loop Until line Is Nothing
reader.Close()
Messagebox.show line all day so I know it is reading the file and the file isn't empty and I have checked the type of line which comes back as string. This makes no sense to me.
Checking for reader.EndOfStream in a While loop will probably work better:
Dim reader As New StreamReader(path)
Dim line As String
While Not reader.EndOfStream
line = reader.ReadLine
selectOptions.Add(line)
End While
reader.Close()
You can also get an exception if selectOptions isn't declared as a New ArrayList, if you properly have all your Options turned On.
Another thing to remember, if your code is in the form's Load Handler, it won't throw an exception it will just break out of the handler routine and load the form. This makes it really hard to find things like bad file names, badly declared objects, etc.
One thing I do is put suspect code in a button's Click handler and see what exceptions it throws there.
Of course this could all be moot if you use the File.ReadAllLines method and add it directly to the ArrayList:
selectOptions.AddRange(File.ReadAllLines(path))
I'm not an IT professional so apologies if I've missed something obvious.
When writing a program I add a class SettingsIni that reads a text file of keys and values. I find this method really flexible as settings can be added or changed without altering any code, regardless of what application I have attached it to.
Here's the main code.
Public Shared Sub Load()
Using settingsReader As StreamReader = New StreamReader(System.AppDomain.CurrentDomain.BaseDirectory & "settings.ini")
Do While settingsReader.Peek > -1
Dim line As String = settingsReader.ReadLine
Dim keysAndValues() As String = line.Split("="c)
settingsTable.Add(keysAndValues(0).Trim, keysAndValues(1).Trim)
Loop
End Using
End Sub
Public Shared Function GetValue(ByVal key As String)
Dim value As String = settingsTable(key)
Return value
End Function
This allows you to use a setting within your code by calling the SettingsIni.GetValue method.
For example:
watcher = New FileSystemWatcher(SettingsIni.GetValue("inputDir"), "*" & SettingsIni.GetValue("extn")).
I find this makes my code esay to read.
My problem is the values in this case, inputDir and extn, are typed freehand and not checked by intellisense. I'm always worried that I may make a typo in an infrequently used branch of an application and miss it during testing.
Is there a best practice method for retrieving settings? or a way around these unchecked freehand typed values?
A best practice for your code example would be to use Constants for the possible settings.
Class Settings
Const inputDir as String = "inputDir"
Const extn as String = "extn"
End Class
watcher = New FileSystemWatcher(SettingsIni.GetValue(Settings.inputDir), "*" & SettingsIni.GetValue(Settings.extn))
I assume you are using VB.NET?
If so, there is the handy "Settings"-menu under "my project". It offers a way to store the settings for your program and retrieve them via "my.settings.YOURKEY". The advantage is, that type securtiy is enforced on this level.
Additionally, you can also store "resources" almost the same way - but resources are better suited for strings / pictures etc. But they are expecially good if you want to translate your program.
As for your current problem:
Store the path in the settings, this way you do not need to change alll your code immidiately but you can use your system and never misspell anything.
If it's a number you could do these 3 things:
Check if is numeric - using IsNumeric function
Check if it is whole number - using Int function, like: if Int(number)=number
Check for the valid range, like: if number>=lowerbound and number<=upperbound
It totally depends on you. You are the one to check almost all the things inside quotes, not the intellisense.
But you still use Try-Catch block:
Try
Dim value As String = settingsTable(key)
Return value
Catch ex As Exception
MsgBox(ex.ToString)
Return ""
End Try
So you will get an message box if you are trying to access a non-existing setting that you may have mistyped.