Question

I have written the application which works in console as well as a user interface. Now when executing the application from a console, I want to show the message in the currently opened console.

static class Program
    {
        [DllImport("kernel32.dll",
            EntryPoint = "GetStdHandle",
            SetLastError = true,
            CharSet = CharSet.Auto,
            CallingConvention = CallingConvention.StdCall)]
        private static extern IntPtr GetStdHandle(int nStdHandle);
        [DllImport("kernel32.dll",
            EntryPoint = "AllocConsole",
            SetLastError = true,
            CharSet = CharSet.Auto,
            CallingConvention = CallingConvention.StdCall)]
        private static extern int AllocConsole();
        private const int STD_OUTPUT_HANDLE = -11;
        private const int MY_CODE_PAGE = 437; 

        [STAThread]
        static void Main(string[] Args)
        {
                if (Args[0] != "")
                {
                    //AllocConsole();
                    commandlineTool(Args[0]);
                }
                else
                {

                    Application.EnableVisualStyles();
                    Application.SetCompatibleTextRenderingDefault(false);
                    Application.Run(new Form2());
                }
static void commandlineTool(string filename)
{
    //all coding here
    AllocConsole();

    IntPtr stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
    SafeFileHandle safeFileHandle = new SafeFileHandle(stdHandle, true);
    FileStream fileStream = new FileStream(safeFileHandle, FileAccess.Write);
    System.Text.Encoding encoding = System.Text.Encoding.GetEncoding(MY_CODE_PAGE);
    StreamWriter standardOutput = new StreamWriter(fileStream, encoding);
    standardOutput.AutoFlush = true;
    Console.SetOut(standardOutput);

    Console.WriteLine("File has been generated.");
    Console.ReadLine();
}

Actually AllocConsole() allocate new console for the process.

But from this a new console opens and shows the message but I want to show the message in the same console.

Answer 1

Method A (preferred, easy):
You can make the application a console application, and release the console if started in GUI mode using FreeConsole. This IMO is the best solution. The only drawback is that the console window will be shown very briefly when starting the application.

Method B (use when necessary):
You can try to attach to the parent process’ console using AttachConsole(ATTACH_PARENT_PROCESS). If the parent process doesn’t have a console this will fail, in which case you’d have to go back to using AllocConsole.

Also if the System.Console class has already been initialized when you try to attach/allocate the console, you’ll have to re-wire the in/out/error streams like this:

    StreamWriter stdOut = new StreamWriter(Console.OpenStandardOutput());
    stdOut.AutoFlush = true;
    Console.SetOut(stdOut);

    StreamWriter stdErr = new StreamWriter(Console.OpenStandardError());
    stdErr.AutoFlush = true;
    Console.SetError(stdErr);

    StreamReader stdIn = new StreamReader(Console.OpenStandardInput());
    Console.SetIn(stdIn);

Otherwise you’ll have no output.