Question

I wonder what the best approach is in implementing a logger which essentially eats all Console.WriteLine() messages and spits out a text file of all these messages.

I know I could use a StringBuilder and populate it with all the messages by doing .AppendLine wherever Console.WriteLine occurs…but I am looking for something more magical than that. Some way using which I don’t have to write as many lines of code as Console.WriteLines in existing code.

And in case you missed the tags, this is for a C#4.0 console application.

Answer 1

I assume what you want is a stream that writes to standard out and to a file. That is, you want everything to still show up on the console, but you also want it to be written to a file. (If you just wanted to redirect output to a file, you could do that from the command line.)

You need to create your own TextWriter-derived class, and have it do the actual output. You call Console.SetOut to make the console write to your TextWriter.

class ConsoleLogger: TextWriter
{
    private TextWriter ConsoleOutputStream;
    private StreamWriter LogOutputStream;
    public ConsoleLogger(string logFilename)
    {
        ConsoleOutputStream = Console.Out;
        // Initialize your log file
        LogOutputStream = new StreamWriter(logFilename);
    }

    public void Write(string s)
    {
        ConsoleOutputStream.Write(s);
        LogOutputStream.Write(s);
    }

    // Other Write functions format their arguments and call Write(string).
}

And in the program that uses this:

private ConsoleLogger MyLogger;
const string LogFilename = "ConsoleLog.txt";
void Main()
{
    MyLogger = new ConsoleLogger(LogFilename);
    Console.SetOut(MyLogger);
}

You don’t have to override all the TextWriter methods. As the documentation says, “A derived class must minimally implement the TextWriter.Write(Char) method to make a useful instance of TextWriter.”

I’ve done something similar to this, and it works quite well.