Logging in C# - To a text file

Question

I am creating a console application and I understand that I need to use ILoggerFactory for logging purpose, but how can I get it to be written to a text file instead to the debug section or the console window.

Answer 1

Hi @Kalpana , Welcome to Microsoft Q&A,

Most of the official examples are for Asp.net core. Do you currently have to use ILoggerFactory? There are currently six official examples of Console output. The link is: Logging in .NET sample source code

You need to create a .Net 7.0 project.

The official example outputs to the console.

You can use StreamWriter to create a txt file, and then Customize ILoggerProvider, writes logs to text file.

The sample code is as follows:

using Microsoft.Extensions.Logging;

class Program
{
    static void Main(string[] args)
    {
        //Define the path to the text file
        string logFilePath = "console_log.txt";

        //Create a StreamWriter to write logs to a text file
        using (StreamWriter logFileWriter = new StreamWriter(logFilePath, append: true))
        {
            //Create an ILoggerFactory
            ILoggerFactory loggerFactory = LoggerFactory.Create(builder =>
            {
                //Add console output
                builder.AddSimpleConsole(options =>
                {
                    options.IncludeScopes = true;
                    options.SingleLine = true;
                    options.TimestampFormat = "HH:mm:ss ";
                });

                //Add a custom log provider to write logs to text files
                builder.AddProvider(new CustomFileLoggerProvider(logFileWriter));
            });

            //Create an ILogger
            ILogger<Program> logger = loggerFactory.CreateLogger<Program>();

            // Output some text on the console
            using (logger.BeginScope("[scope is enabled]"))
            {
                logger.LogInformation("Hello World!");
                logger.LogInformation("Logs contain timestamp and log level.");
                logger.LogInformation("Each log message is fit in a single line.");
            }
        }

        //your application code

        Console.WriteLine("Press any key to exit...");
        Console.ReadKey();
    }
}

// Customized ILoggerProvider, writes logs to text files
public class CustomFileLoggerProvider : ILoggerProvider
{
    private readonly StreamWriter _logFileWriter;

    public CustomFileLoggerProvider(StreamWriter logFileWriter)
    {
        _logFileWriter = logFileWriter ?? throw new ArgumentNullException(nameof(logFileWriter));
    }

    public ILogger CreateLogger(string categoryName)
    {
        return new CustomFileLogger(categoryName, _logFileWriter);
    }

    public void Dispose()
    {
        _logFileWriter.Dispose();
    }
}

// Customized ILogger, writes logs to text files
public class CustomFileLogger : ILogger
{
    private readonly string _categoryName;
    private readonly StreamWriter _logFileWriter;

    public CustomFileLogger(string categoryName, StreamWriter logFileWriter)
    {
        _categoryName = categoryName;
        _logFileWriter = logFileWriter;
    }

    public IDisposable BeginScope<TState>(TState state)
    {
        return null;
    }

    public bool IsEnabled(LogLevel logLevel)
    {
        // Ensure that only information level and higher logs are recorded
        return logLevel >= LogLevel.Information;
    }

    public void Log<TState>(
        LogLevel logLevel,
        EventId eventId,
        TState state,
        Exception exception,
        Func<TState, Exception, string> formatter)
    {
        // Ensure that only information level and higher logs are recorded
        if (!IsEnabled(logLevel))
        {
            return;
        }

        // Get the formatted log message
        var message = formatter(state, exception);

        //Write log messages to text file
        _logFileWriter.WriteLine($"[{logLevel}] [{_categoryName}] {message}");
        _logFileWriter.Flush();
    }
}

Best Regards,

Jiale

---

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Answer 2

You might consider using SeriLog which can be setup so that say each day a new text file is created. Following below to setup where a folder LogFiles is created under, in this case the Debug folder and sub folders for each day the Log.xxxx is executed.

Install the follow NuGet packages

• SeriLog
• Serilog.Sinks.File

Add the following class which runs automatically because of ModuleInitializer.

using System.Runtime.CompilerServices;
using Serilog;

namespace TODO;

#pragma warning disable CS8602
public class SetupLogging
{
    [ModuleInitializer]
    public static void Init()
    {
        Initialize();
    }
    public static void Initialize()
    {

        Log.Logger = new LoggerConfiguration()
            .MinimumLevel.Verbose()
            .WriteTo.File(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "LogFiles", $"{DateTime.Now.Year}-{DateTime.Now.Month}-{DateTime.Now.Day}", "Log.txt"),
                rollingInterval: RollingInterval.Infinite,
                outputTemplate: "[{Timestamp:yyyy-MM-dd HH:mm:ss.fff} [{Level}] {Message}{NewLine}{Exception}")
            .CreateLogger();
    }
}

Now to log

Log.Information("TODO");
Log.Error(new Exception("Fake exception"),"TODO");

Screenshot

Example logs

[2023-09-22 02:33:43.538 [Error] Foo
System.IO.DirectoryNotFoundException: Could not find a part of the path 'C:\OED\DotnetLand\VS2022\CodeExperiments\WinFormsApp1\bin\Debug\net7.0-windows\TestFile.txt\!'.
   at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options)
   at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.Strategies.OSFileStreamStrategy..ctor(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.Strategies.FileStreamHelpers.ChooseStrategyCore(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.StreamReader.ValidateArgsAndOpenPath(String path, Encoding encoding, Int32 bufferSize)
   at System.IO.File.ReadAllText(String path, Encoding encoding)
   at WinFormsApp1.Form1.button2_Click(Object sender, EventArgs e) in ./Form1.cs:line 41

And

[2023-09-29 02:27:20.267 [Information] Hello

This works with console, windows forms and even web projects.

Answer 3

A very simple solution can be this one:

StreamWriter sw = File.AppendText("logfile.txt");

// this is important
sw.AutoFlush = true;

Console.SetError(sw);
Console.Error.WriteLine("This goes to the file.");

// if you set error to Out, the next line will go to the console screen
Console.SetError(Console.Out);
Console.Error.WriteLine("This goes to the screen.");