Develop Reference

Read and write from/to the same line with BinaryReader/BinaryWriter

I want to read a binary file line by line (I'm writing of course continously, but I know that after 457 bytes new data start and I know exactly the byte structure and where which information is written to) and change a special entry of the line. I get an System.IO.IOException when I try to access the same file with both BinaryReader and BinaryWriter. I use locking to prevent that the file is accessed from somewhere else.
My code is:
using (FileStream fs2 = new FileStream(testfile, FileMode.Open, FileAccess.Read))
{
using (BinaryReader r = new BinaryReader(fs2))
{
using (BinaryWriter bw = new BinaryWriter(new FileStream(testfile, FileMode.Open, FileAccess.Write), utf8))
{
for (int i = 0; i < 11000; i+=457)
{
int myint = r.ReadInt64();
bw.Seek(i, SeekOrigin.Current);
bw.Write(myint*2);
}
}
}
}
How can I do this?

Do not create the second FileStream because the file is locked for the read operation by the first FileStream object.
If you are sure about file structure, the exception only can come out from 2nd FileStream instantiation. See link below for more information:
Read and Write to File at the same time

It is working for me using the following code:
if (File.Exists(testfile))
{
FileInfo fi = new FileInfo(testfile);
using (FileStream fs2 = new FileStream(testfile, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (BinaryReader r = new BinaryReader(fs2))
{
r.BaseStream.Seek(0, SeekOrigin.Begin);
using (BinaryWriter bw = new BinaryWriter(new FileStream(testfile, FileMode.Open, FileAccess.Write, FileShare.ReadWrite)))
{
for (int i = 0; i <= (fi.Length-177); i += 177)//181
{
}
}
}
}
}

System.IO.MemoryStream cannot access a closed file

I'm new to Streams and in the program i'm developing requires reading data from a hex file.
File=level.dat
The code im using:
FileStream fs;
private void Form1_Load(object sender, EventArgs e)
{
Main("PCWorld\\level.dat");
NbtTree nbtTree = new NbtTree();
Stream s = fs;
Stream destStream = new MemoryStream();
nbtTree.ReadFrom(s);
nbtTree.WriteTo(destStream);
}
void Main():
void Main(string filename)
{
// From MSDN Forums, slightly modified by me
try
{
string fileName = filename;
// Create random data to write to the file.
byte[] dataArray = new byte[100000];
new Random().NextBytes(dataArray);
using (FileStream
fileStream = new FileStream(fileName, FileMode.Create))
{
// Write the data to the file, byte by byte.
for (int i = 0; i < dataArray.Length; i++)
{
fileStream.WriteByte(dataArray[i]);
}
// Set the stream position to the beginning of the file.
fileStream.Seek(0, SeekOrigin.Begin);
// Read and verify the data.
for (int i = 0; i < fileStream.Length; i++)
{
if (dataArray[i] != fileStream.ReadByte())
{
MessageBox.Show("Failed to load " + fileName + " (MCPC.dll)\n\nReason: Failed to read bytes\nResult: Close();\nSoloution: Try again and/or tell DMP9 Software", "Error");
Close();
return;
}
fs = fileStream;
}
}
}
catch (OutOfMemoryException ex)
{
MessageBox.Show("Failed to load NBT++.PC.exe\n\nReason: Out of memory (System.OutOfMemoryException: " + ex.Message + ")\nResult: Close();\nSoloution: Your PC Does not have enough RAM to run NBT++", "Error");
Close();
}
}
My program has a reference of Substrate (https://code.google.com/p/substrate-minecraft/downloads/list) and that does most of the work, but its my code giving
the "Cannot access a closed file"
Any help?
Thanks...

Your problem is in:
Stream s = fs;
The fs filestream is closed in your Main method (using statement disposes the filestream). To fix this you should open a new filestream to read from the file:
Stream s = new FileStream("PCWorld\\level.dat", FileMode.Read);

When using
using (FileStream fileStream = new FileStream(fileName, FileMode.Create))
{...}
you are closing this filestream when you go out scope. So you have to re-open file to read
http://msdn.microsoft.com/en-us/library/yh598w02.aspx

FileMode and FileAccess and IOException: The process cannot access the file 'filename' because it is being used by another process

I have an application A that generates a text file for tracing.
While, an application B needs read the same text file and attach in a mailmessage.
But I get the following error, when application B try read the text file:
IOException: The process cannot access the file 'filename' because it
is being used by another process
Any suggestions ? Maybe better use for FileMode and FileAccess?
Application A
if (File.Exists(nFile2)) File.Delete(nFile2);
traceFile2 = File.Open(nFile2, FileMode.Create, FileAccess.ReadWrite, FileShare.ReadWrite);
if (traceFile2 != null)
{
var twt2 = new TextWriterTraceListener(traceFile2);
// http://www.helixoft.com/blog/archives/20
try
{
if (twt2.Writer is StreamWriter)
{
(twt2.Writer as StreamWriter).AutoFlush = true;
}
}
catch { }
var indiceTraceFile2 = Trace.Listeners.Add(twt2);
System.Diagnostics.Trace.WriteLine("INICIO: " + DateTime.Now.ToString());
Application B
using (FileStream fileStream = File.Open(f, FileMode.Open, FileAccess.ReadWrite, FileShare.Read))
{
var messageAttachment = new Attachment(fileStream, Path.GetFileName(f));
msgMail.Attachments.Add(messageAttachment);
}

You need to make sure that both the service and the reader open the log file non-exclusively. Notice line 2 of App A and Line 1 of App B
Application A:
if (File.Exists(nFile2))
File.Delete(nFile2);
traceFile2 = new FileStream(nFile2, FileMode.Open, FileAccess.Write, FileShare.ReadWrite);
if (traceFile2 != null)
{
var twt2 = new TextWriterTraceListener(traceFile2);
// http://www.helixoft.com/blog/archives/20
try
{
if (twt2.Writer is StreamWriter)
{
(twt2.Writer as StreamWriter).AutoFlush = true;
}
}
catch { }
var indiceTraceFile2 = Trace.Listeners.Add(twt2);
System.Diagnostics.Trace.WriteLine("INICIO: " + DateTime.Now.ToString());
and Application B:
using (FileStream fileStream = new FileStream(f, FileMode.Open,
FileAccess.Read,
FileShare.ReadWrite))
{
var messageAttachment = new Attachment(fileStream, Path.GetFileName(f));
msgMail.Attachments.Add(messageAttachment);
}

Of course you can read and write from/to the same file at the same time (by different threads/processes).
Here is a sample code. Just see how FileStream is created.
string fname = "a.txt";
//WRITER
Task.Factory.StartNew(() =>
{
var f = new FileStream(fname, FileMode.OpenOrCreate, FileAccess.Write, FileShare.ReadWrite);
var s = new StreamWriter(f);
long l = 0;
while (true)
{
s.WriteLine(l++);
s.Flush();
Task.Delay(1000).Wait();
}
});
//READER
Task.Factory.StartNew(() =>
{
Task.Delay(1000).Wait();
var f = new FileStream(fname, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
var s = new StreamReader(f);
while (true)
{
var line = s.ReadLine();
if (line == null) { Task.Delay(100).Wait(); continue; };
Console.WriteLine("> " + line + " <");
}
});

It seems that you are not using the Dispose() and Close() methods of StreamWriter class to release the file.

You need to release control of the file from Program A. Try closing or disposing the streamwriter when you finish.
Or you might attempt using as is described in the answer to this question: Releasing access to files

Windows Phone C# -loading from text files

I have my program save the contents of 4 different text boxes into 4 separate text files using IsolatedStorageFile. This works fine, until I have to load them later. When I'm loading, all 4 text files are loaded into the first text box, and the remaining 3 are left blank.
Here's the code I'm using to save the files:
private void Button_Click_2(object sender, RoutedEventArgs e)
{
defaultPicker.ItemsSource = new List<string>() { { box1.Text }, { box2.Text }, { box3.Text }, { box4.Text } };
//Deletes any previous saved files
IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication();
storage.DeleteFile("ip-1.txt");
storage.DeleteFile("ip-2.txt");
storage.DeleteFile("ip-3.txt");
storage.DeleteFile("ip-4.txt");
// This saves users IP's into text files for later loading
IsolatedStorageFile fileStorage = IsolatedStorageFile.GetUserStoreForApplication();
StreamWriter Writer = new StreamWriter(new IsolatedStorageFileStream("ip-1.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box1.Text);
new StreamWriter(new IsolatedStorageFileStream("ip-2.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box2.Text);
new StreamWriter(new IsolatedStorageFileStream("ip-3.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box3.Text);
new StreamWriter(new IsolatedStorageFileStream("ip-4.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box4.Text);
Writer.Close();
}
and to load the files later:
private void Button_Click_4(object sender, RoutedEventArgs e)
{
// Loads IP's from text file or displays error message
//First clear the boxes...
box1.Text = "";
box2.Text = "";
box3.Text = "";
box4.Text = "";
//Load from text files...
IsolatedStorageFile fileStorage = IsolatedStorageFile.GetUserStoreForApplication();
StreamReader Reader = null;
try
{
Reader = new StreamReader(new IsolatedStorageFileStream("ip-1.txt", FileMode.Open, fileStorage));
string textFile = Reader.ReadToEnd();
box1.Text = textFile;
}
catch
{
}
IsolatedStorageFile.GetUserStoreForApplication();
try
{
Reader = new StreamReader(new IsolatedStorageFileStream("ip-2.txt", FileMode.Open, fileStorage));
string textFile2 = Reader.ReadToEnd();
box2.Text = textFile2;
}
catch
{
}
IsolatedStorageFile.GetUserStoreForApplication();
try
{
Reader = new StreamReader(new IsolatedStorageFileStream("ip-3.txt", FileMode.Open, fileStorage));
string textFile3 = Reader.ReadToEnd();
box3.Text = textFile3;
}
catch
{
}
IsolatedStorageFile.GetUserStoreForApplication();
try
{
Reader = new StreamReader(new IsolatedStorageFileStream("ip-4.txt", FileMode.Open, fileStorage));
string textFile4 = Reader.ReadToEnd();
box4.Text = textFile4;
Reader.Close();
}
catch
{
}
// To sync with ListPicker
defaultPicker.ItemsSource = new List<string>() { { box1.Text }, { box2.Text }, { box3.Text }, { box4.Text } };
}
Any help into the right direction would be appreciated.

First, I suggest you stop eating all exceptions. At least in debug mode, have the empty catch blocks in a pragma.
I would drop the single declaration of Reader and create a new one per file:
try
{
using (StreamReader reader = new StreamReader(new IsolatedStorageFileStream("ip-1.txt", FileMode.Open, fileStorage)))
{
string textFile = reader.ReadToEnd();
box1.Text = textFile;
}
}

You aren't writing to the four files correctly. You need to reassign your Writer each time.
StreamWriter Writer = new StreamWriter(new IsolatedStorageFileStream("ip-1.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box1.Text);
Writer = new StreamWriter(new IsolatedStorageFileStream("ip-2.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box2.Text);
Writer = new StreamWriter(new IsolatedStorageFileStream("ip-3.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box3.Text);
Writer = new StreamWriter(new IsolatedStorageFileStream("ip-4.txt", FileMode.OpenOrCreate, fileStorage));
Writer.WriteLine(box4.Text);
Writer.Close();
In the future you should have something in your catch blocks to display any caught exceptions. In this case it would have told you that the three other files weren't able to be loaded because they didn't exist.

Reading file content changes in .NET

In Linux, a lot of IPC is done by appending to a file in 1 process and reading the new content from another process.
I want to do the above in Windows/.NET (Too messy to use normal IPC such as pipes). I'm appending to a file from a Python process, and I want to read the changes and ONLY the changes each time FileSystemWatcher reports an event. I do not want to read the entire file content into memory each time I'm looking for changes (the file will be huge)
Each append operation appends a row of data that starts with a unique incrementing counter (timestamp+key) and ends with a newline.

using (FileStream fs = new FileStream
(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (StreamReader sr = new StreamReader(fs))
{
while (someCondition)
{
while (!sr.EndOfStream)
ProcessLinr(sr.ReadLine());
while (sr.EndOfStream)
Thread.Sleep(100);
ProcessLinr(sr.ReadLine());
}
}
}
this will help you read only appended lines

You can store the offset of the last read operation and seek the file to that offset when you get a changed file notification. An example follows:
Main method:
public static void Main(string[] args)
{
File.WriteAllLines("test.txt", new string[] { });
new Thread(() => ReadFromFile()).Start();
WriteToFile();
}
Read from file method:
private static void ReadFromFile()
{
long offset = 0;
FileSystemWatcher fsw = new FileSystemWatcher
{
Path = Environment.CurrentDirectory,
Filter = "test.txt"
};
FileStream file = File.Open(
"test.txt",
FileMode.Open,
FileAccess.Read,
FileShare.Write);
StreamReader reader = new StreamReader(file);
while (true)
{
fsw.WaitForChanged(WatcherChangeTypes.Changed);
file.Seek(offset, SeekOrigin.Begin);
if (!reader.EndOfStream)
{
do
{
Console.WriteLine(reader.ReadLine());
} while (!reader.EndOfStream);
offset = file.Position;
}
}
}
Write to file method:
private static void WriteToFile()
{
for (int i = 0; i < 100; i++)
{
FileStream writeFile = File.Open(
"test.txt",
FileMode.Append,
FileAccess.Write,
FileShare.Read);
using (FileStream file = writeFile)
{
using (StreamWriter sw = new StreamWriter(file))
{
sw.WriteLine(i);
Thread.Sleep(100);
}
}
}
}