How to truncate a file in c#?

I am writing actions done by the program in C# into a file by using Trace.Writeln() function. But the file is becoming too large. How to truncate this file when it grows to 1MB?

TextWriterTraceListener traceListener = new TextWriterTraceListener(File.AppendText("audit.txt"));
Trace.Listeners.Add(traceListener);
Trace.AutoFlush = true;

What sh开发者_如何转开发ould be added to the above block

Try to play around with FileStream.SetLength

FileStream fileStream = new FileStream(...);
fileStream.SetLength(sizeInBytesNotChars);

Close the file and then reopen it using FileMode.Truncate.

Some log implementations archive the old file under an old name before reopening it, to preserve a larger set of data without any file getting too big.

As opposed to trying to do this yourself, I'd really recommend using something like log4net; it has a lot of this sort of useful functionality built in.

When the file is over 500000 bytes, it will cut the beginning 250000 bytes off from the file so the remaining file is 250000 bytes long.

FileStream fs = new FileStream(strFileName, FileMode.OpenOrCreate);
        if (fs.Length > 500000)
        {
            // Set the length to 250Kb
            Byte[] bytes = new byte[fs.Length];
            fs.Read(bytes, 0, (int)fs.Length);
            fs.Close();
            FileStream fs2 = new FileStream(strFileName, FileMode.Create);
            fs2.Write(bytes, (int)bytes.Length - 250000, 250000);
            fs2.Flush();
        } // end if (fs.Length > 500000) 

By doing this:

if(new FileInfo("<your file path>").Length > 1000000)
{
    File.WriteAllText("<your file path>", "");
}

If you have no desire to keep the contents, or move them into a subsidiary file that tracks the update for the cycle (whether by day or some other cycle length), I would recommend just rewriting the file using this simple method:

    private void Truncate(readFile)     // to clear contents of file and note last time it was cleared
    {
        string readFile = readPath + ".txt";
        string str = string.Format("{0} : Truncated Contents", DateTime.Now.ToString("dd/MM/yyyy hh:mm:ss tt"));
        using (StreamWriter truncate = new StreamWriter(readFile))
        {
            truncate.WriteLine(str); // truncates and leaves the message with DateTime stamp
        }
    }

If, on the other hand, you want to save the contents to a file for the date they were truncated, you can use the following method in conjunction with the above:

    private void Truncate(readPath)     // to clear contents of file, copy, and note last time it was cleared and copied
    {
        if (!File.Exists(readPath))    // create the new file for storing old entries
        {
            string readFile = readPath + ".txt";
            string writeFile = readPath + DateTime.Now.ToString("_dd-MM-yyyy_hh-mm") + ".txt"; // you can add all the way down to milliseconds if your system runs fast enough
            using (FileStream fs = new FileStream(writeFile, FileMode.OpenOrCreate, FileAccess.Write))
            {
                using (StreamWriter write = new StreamWriter(fs))
                using (StreamReader file = new StreamReader(readFile))
                {
                    write.WriteLine(string.Format(textA, DateTime.Now.ToString("dd/MM/yyyy hh:mm:ss tt")));
                    string line;
                    var sb = new StringBuilder();
                    while ((line = file.ReadLine()) != null)
                    {
                        line = line.Replace("\0", ""); // removes nonsense bits from stream
                        sb.AppendLine(line);
                    }
                    write.WriteLine(sb.ToString());
                    string textB = "{0} : Copied Source";
                    write.WriteLine(string.Format(textB, DateTime.Now.ToString("dd/MM/yyyy hh:mm:ss tt")));
                }
            }
            string str = string.Format("{0} : Truncated Contents", DateTime.Now.ToString("dd/MM/yyyy hh:mm:ss tt"));
            using (StreamWriter truncate = new StreamWriter(readFile))
            {
                truncate.WriteLine(str); // truncates and leaves the message with DateTime stamp
            }
        }
    }

Either way, you can utilize the method of your choice with the following block:

if(new FileInfo("audit.txt").Length >= 0xfffff) // hex for 1MB
{
    Truncate("audit");
}

I hope this helps future readers.

Thanks,

C§

Perhaps this would be simple solution:

// Test the file is more or equal to a 1MB ((1 * 1024) * 1024)
// There are 1024B in 1KB, 1024KB in 1MB
if (new FileInfo(file).length >= ((1 * 1024) * 1024))
{
    // This will open your file. Once opened, it will write all data to 0
    using (FileStream fileStream = new FileStream(file, FileMode.Truncate, FileAccess.Write))
    {
        // Write to your file.
    }
}

Late answer, but you might try:

StreamWriter sw = new StreamWriter(YourFileName, false);
sw.Write("");
sw.Flush();
sw.Close();

Sending false as the second param of StreamWriter() tells it NOT to append, resulting in it overwriting the file. In this case with an empty string, effectively truncating it.