C#setin, setout, seterror的用法…！！

C#setin, setout, seterror的用法…！！

public class InsertTabs {
    private const int tabSize = 4;
    private const string usageText = "Usage: INSERTTABS inputfile.txt outputfile.txt";
    public static int Main(string[] args) {
        StreamWriter writer = null;

        if (args.Length             Console.WriteLine(usageText);
            return 1;
        }

        try {
            writer = new StreamWriter(args[1]);
            Console.SetOut(writer);
            Console.SetIn(new StreamReader(args[0]));
        }
        catch(IOException e) {
            TextWriter errorWriter = Console.Error;
            errorWriter.WriteLine(e.Message);
            errorWriter.WriteLine(usageText);
            return 1;            
        }
        string line;
        while ((line = Console.ReadLine()) != null) {
            string newLine = line.Replace(("").PadRight(tabSize, ' '), "\t");
            Console.WriteLine(newLine);
        }
        writer.Close();
        // Recover the standard output stream so that a 
        // completion message can be displayed.
        StreamWriter standardOutput = new StreamWriter(Console.OpenStandardOutput());
        standardOutput.AutoFlush = true;
        Console.SetOut(standardOutput);
        Console.WriteLine("INSERTTABS has completed the processing of {0}.", args[0]);
        return 0;
    }
}