Tutorial :How do I create a C# app that decides itself whether to show as a console or windowed app?


Is there a way to launch a C# application with the following features?

  1. It determines by command-line parameters whether it is a windowed or console app
  2. It doesn't show a console when it is asked to be windowed and doesn't show a GUI window when it is running from the console.

For example,

myapp.exe /help
would output to stdout on the console you used, but
by itself would launch my Winforms or WPF user interface.

The best answers I know of so far involve having two separate exe and use IPC, but that feels really hacky.

What options do I have and trade-offs can I make to get the behavior described in the example above? I'm open to ideas that are Winform-specific or WPF-specific, too.


Make the app a regular windows app, and create a console on the fly if needed.

More details at this link (code below from there)

using System;  using System.Windows.Forms;    namespace WindowsApplication1 {    static class Program {      [STAThread]      static void Main(string[] args) {        if (args.Length > 0) {          // Command line given, display console          if ( !AttachConsole(-1) ) { // Attach to an parent process console             AllocConsole(); // Alloc a new console          }            ConsoleMain(args);        }        else {          Application.EnableVisualStyles();          Application.SetCompatibleTextRenderingDefault(false);          Application.Run(new Form1());        }      }      private static void ConsoleMain(string[] args) {        Console.WriteLine("Command line = {0}", Environment.CommandLine);        for (int ix = 0; ix < args.Length; ++ix)          Console.WriteLine("Argument{0} = {1}", ix + 1, args[ix]);        Console.ReadLine();      }        [System.Runtime.InteropServices.DllImport("kernel32.dll")]      private static extern bool AllocConsole();        [System.Runtime.InteropServices.DllImport("kernel32.dll")]      private static extern bool AttachConsole(int pid);      }  }  


I basically do that the way depicted in Eric's answer, additionally I detach the console with FreeConsole and use the SendKeys command to get the command prompt back.

    [DllImport("kernel32.dll")]      private static extern bool AllocConsole();        [DllImport("kernel32.dll")]      private static extern bool AttachConsole(int pid);        [DllImport("kernel32.dll", SetLastError = true)]      private static extern bool FreeConsole();        [STAThread]      static void Main(string[] args)      {          if (args.Length > 0 && (args[0].Equals("/?") || args[0].Equals("/help", StringComparison.OrdinalIgnoreCase)))          {              // get console output              if (!AttachConsole(-1))                  AllocConsole();                ShowHelp(); // show help output with Console.WriteLine              FreeConsole(); // detach console                // get command prompt back              System.Windows.Forms.SendKeys.SendWait("{ENTER}");                 return;          }            // normal winforms code          Application.EnableVisualStyles();          Application.SetCompatibleTextRenderingDefault(false);          Application.Run(new MainForm());        }  


Write two apps (one console, one windows) and then write another smaller app which based on the parameters given opens up one of the other apps (and then would presumably close itself since it would no longer be needed)?


I've done this by creating two separate apps.

Create the WPF app with this name: MyApp.exe. And create the console app with this name: MyApp.com. When you type your app name in the command line like this MyApp or MyApp /help (without .exe extension) the console app with the .com extension will take precedence. You can have your console application invoke the MyApp.exe according to the parameters.

This is exactly how devenv behaves. Typing devenv at the command line will launch Visual Studio's IDE. If you pass parameters like /build, it will remain in the command line.


NOTE: I haven't tested this, but I believe it would work...

You could do this:

Make your app a windows forms application. If you get a request for console, don't show your main form. Instead, use platform invoke to call into the Console Functions in the Windows API and allocate a console on the fly.

(Alternatively, use the API to hide the console in a console app, but you'd probably see the console "flicker" as it was created in this case...)


As far as I am aware there is a flag in the exe that tells it whether to run as console or windowed app. You can flick the flag with tools that come with Visual Studio, but you cann't do this at runtime.

If the exe is compiled as a console, then it will always open a new console if its not started from one. If the the exe is an application then it can't output to the console. You can spawn a separate console - but it won't behave like a console app.

I the past we have used 2 separate exe's. The console one being a thin wrapper over the forms one (you can reference an exe as you would reference a dll, and you can use the [assembly:InternalsVisibleTo("cs_friend_assemblies_2")] attribute to trust the console one, so you don't have to expose more than you need to).


I would create a solution that is a Windows Form App since there are two functions you can call that will hook into the current console. So you can treat the program like a console program. or by default you can launch the GUI.

The AttachConsole function will not create a new console. For more information about AttachConsole, check out PInvoke: AttachConsole

Below a sample program of how to use it.

using System.Runtime.InteropServices;    namespace Test  {      /// <summary>      /// This function will attach to the console given a specific ProcessID for that Console, or      /// the program will attach to the console it was launched if -1 is passed in.      /// </summary>      [DllImport("kernel32.dll", SetLastError = true)]      private static extern bool AttachConsole(int dwProcessId);        [DllImport("kernel32.dll", SetLastError = true)]      private static extern bool FreeConsole();          [STAThread]      public static void Main()       {             Application.ApplicationExit +=new EventHandler(Application_ApplicationExit);          string[] commandLineArgs = System.Environment.GetCommandLineArgs();            if(commandLineArgs[0] == "-cmd")          {              //attaches the program to the running console to map the output              AttachConsole(-1);          }          else          {              //Open new form and do UI stuff              Form f = new Form();              f.ShowDialog();          }        }        /// <summary>      /// Handles the cleaning up of resources after the application has been closed      /// </summary>      /// <param name="sender"></param>      public static void Application_ApplicationExit(object sender, System.EventArgs e)      {          FreeConsole();      }  }  


Maybe this link will provide some insight into what you are looking to do.


One way to do this is to write a Window app that doesn't show a window if the command line arguments indicate it shouldn't.

You can always get the command line arguments and check them before showing the first window.


The important thing to remember to do after AttachConsole() or AllocConsole() calls to get it to work in all cases is:

if (AttachConsole(ATTACH_PARENT_PROCESS))    {      System.IO.StreamWriter sw =        new System.IO.StreamWriter(System.Console.OpenStandardOutput());      sw.AutoFlush = true;      System.Console.SetOut(sw);      System.Console.SetError(sw);    }  

I have found that works with or without VS hosting process. With output being sent with System.Console.WriteLine or System.Console.out.WriteLine before call To AttachConsole or AllocConsole. I have included my method below:

public static bool DoConsoleSetep(bool ClearLineIfParentConsole)  {    if (GetConsoleWindow() != System.IntPtr.Zero)    {      return true;    }    if (AttachConsole(ATTACH_PARENT_PROCESS))    {      System.IO.StreamWriter sw = new System.IO.StreamWriter(System.Console.OpenStandardOutput());      sw.AutoFlush = true;      System.Console.SetOut(sw);      System.Console.SetError(sw);      ConsoleSetupWasParentConsole = true;      if (ClearLineIfParentConsole)      {        // Clear command prompt since windows thinks we are a windowing app        System.Console.CursorLeft = 0;        char[] bl = System.Linq.Enumerable.ToArray<char>(System.Linq.Enumerable.Repeat<char>(' ', System.Console.WindowWidth - 1));        System.Console.Write(bl);        System.Console.CursorLeft = 0;      }      return true;    }    int Error = System.Runtime.InteropServices.Marshal.GetLastWin32Error();    if (Error == ERROR_ACCESS_DENIED)    {      if (log.IsDebugEnabled) log.Debug("AttachConsole(ATTACH_PARENT_PROCESS) returned ERROR_ACCESS_DENIED");      return true;    }    if (Error == ERROR_INVALID_HANDLE)    {      if (AllocConsole())      {        System.IO.StreamWriter sw = new System.IO.StreamWriter(System.Console.OpenStandardOutput());        sw.AutoFlush = true;        System.Console.SetOut(sw);        System.Console.SetError(sw);        return true;      }    }    return false;  }  

I also called this when I was done in case I needed command prompt to redisplay when I was done doing output.

public static void SendConsoleInputCR(bool UseConsoleSetupWasParentConsole)  {    if (UseConsoleSetupWasParentConsole && !ConsoleSetupWasParentConsole)    {      return;    }    long LongNegOne = -1;    System.IntPtr NegOne = new System.IntPtr(LongNegOne);    System.IntPtr StdIn = GetStdHandle(STD_INPUT_HANDLE);    if (StdIn == NegOne)    {      return;    }    INPUT_RECORD[] ira = new INPUT_RECORD[2];    ira[0].EventType = KEY_EVENT;    ira[0].KeyEvent.bKeyDown = true;    ira[0].KeyEvent.wRepeatCount = 1;    ira[0].KeyEvent.wVirtualKeyCode = 0;    ira[0].KeyEvent.wVirtualScanCode = 0;    ira[0].KeyEvent.UnicodeChar = '\r';    ira[0].KeyEvent.dwControlKeyState = 0;    ira[1].EventType = KEY_EVENT;    ira[1].KeyEvent.bKeyDown = false;    ira[1].KeyEvent.wRepeatCount = 1;    ira[1].KeyEvent.wVirtualKeyCode = 0;    ira[1].KeyEvent.wVirtualScanCode = 0;    ira[1].KeyEvent.UnicodeChar = '\r';    ira[1].KeyEvent.dwControlKeyState = 0;    uint recs = 2;    uint zero = 0;    WriteConsoleInput(StdIn, ira, recs, out zero);  }  

Hope this helps...


No 1 is easy.

No 2 can't be done, I don't think.

The docs say:

Calls to methods such as Write and WriteLine have no effect in Windows applications.

The System.Console class is initialized differently in console and GUI applications. You can verify this by looking at the Console class in the debugger in each application type. Not sure if there's any way to re-initialize it.

Demo: Create a new Windows Forms app, then replace the Main method with this:

    static void Main(string[] args)      {          if (args.Length == 0)          {              Application.EnableVisualStyles();              Application.SetCompatibleTextRenderingDefault(false);              Application.Run(new Form1());          }          else          {              Console.WriteLine("Console!\r\n");          }      }  

The idea is that any command line parameters will print to the console and exit. When you run it with no arguments, you get the window. But when you run it with a command line argument, nothing happens.

Then select the project properties, change the project type to "Console Application", and recompile. Now when you run it with an argument, you get "Console!" like you want. And when you run it (from the command line) with no arguments, you get the window. But the command prompt won't return until you exit the program. And if you run the program from Explorer, a command window will open and then you get a window.


I have worked out a way to do this including using stdin, but I must warn you that it is not pretty.

The problem with using stdin from an attached console is that the shell will also read from it. This causes the input to sometimes go to your app but sometimes to the shell.

The solution is to block the shell for the duration of the apps lifetime (although technically you could try to block it only when you need input). The way I choose to do this is by sending keystrokes to the shell to run a powershell command that waits for the app to terminate.

Incidentally this also fixes the problem of the prompt not getting back after the app terminates.

I have briefly attempted to get it to work from the powershell console as well. The same principles apply, but I didn't get it to execute my command. It might be that powershell has some security checks to prevent running commands from other applications. Because I don't use powershell much I didn't look into it.

    [DllImport("kernel32.dll", SetLastError = true)]      private static extern bool AllocConsole();        [DllImport("kernel32", SetLastError = true)]      private static extern bool AttachConsole(int dwProcessId);        private const uint STD_INPUT_HANDLE = 0xfffffff6;      private const uint STD_OUTPUT_HANDLE = 0xfffffff5;      private const uint STD_ERROR_HANDLE = 0xfffffff4;        [DllImport("kernel32.dll")]      private static extern IntPtr GetStdHandle(uint nStdHandle);      [DllImport("Kernel32.dll", SetLastError = true)]      public static extern int SetStdHandle(uint nStdHandle, IntPtr handle);        [DllImport("kernel32.dll", SetLastError = true)]      private static extern int GetConsoleProcessList(int[] ProcessList, int ProcessCount);        [DllImport("user32.dll")]      public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);      [DllImport("user32.dll")]      public static extern IntPtr PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);        /// <summary>      /// Attach to existing console or create new. Must be called before using System.Console.      /// </summary>      /// <returns>Return true if console exists or is created.</returns>      public static bool InitConsole(bool createConsole = false, bool suspendHost = true) {            // first try to attach to an existing console          if (AttachConsole(-1)) {              if (suspendHost) {                  // to suspend the host first try to find the parent                  var processes = GetConsoleProcessList();                    Process host = null;                  string blockingCommand = null;                    foreach (var proc in processes) {                      var netproc = Process.GetProcessById(proc);                      var processName = netproc.ProcessName;                      Console.WriteLine(processName);                      if (processName.Equals("cmd", StringComparison.OrdinalIgnoreCase)) {                          host = netproc;                          blockingCommand = $"powershell \"& wait-process -id {Process.GetCurrentProcess().Id}\"";                      } else if (processName.Equals("powershell", StringComparison.OrdinalIgnoreCase)) {                          host = netproc;                          blockingCommand = $"wait-process -id {Process.GetCurrentProcess().Id}";                      }                  }                    if (host != null) {                      // if a parent is found send keystrokes to simulate a command                      var cmdWindow = host.MainWindowHandle;                      if (cmdWindow == IntPtr.Zero) Console.WriteLine("Main Window null");                        foreach (char key in blockingCommand) {                          SendChar(cmdWindow, key);                          System.Threading.Thread.Sleep(1); // required for powershell                      }                        SendKeyDown(cmdWindow, Keys.Enter);                        // i haven't worked out how to get powershell to accept a command, it might be that this is a security feature of powershell                      if (host.ProcessName == "powershell") Console.WriteLine("\r\n *** PRESS ENTER ***");                  }              }                return true;          } else if (createConsole) {              return AllocConsole();          } else {              return false;          }      }        private static void SendChar(IntPtr cmdWindow, char k) {          const uint WM_CHAR = 0x0102;            IntPtr result = PostMessage(cmdWindow, WM_CHAR, ((IntPtr)k), IntPtr.Zero);      }        private static void SendKeyDown(IntPtr cmdWindow, Keys k) {          const uint WM_KEYDOWN = 0x100;          const uint WM_KEYUP = 0x101;            IntPtr result = SendMessage(cmdWindow, WM_KEYDOWN, ((IntPtr)k), IntPtr.Zero);          System.Threading.Thread.Sleep(1);          IntPtr result2 = SendMessage(cmdWindow, WM_KEYUP, ((IntPtr)k), IntPtr.Zero);      }        public static int[] GetConsoleProcessList() {          int processCount = 16;          int[] processList = new int[processCount];            // supposedly calling it with null/zero should return the count but it didn't work for me at the time          // limiting it to a fixed number if fine for now          processCount = GetConsoleProcessList(processList, processCount);          if (processCount <= 0 || processCount >= processList.Length) return null; // some sanity checks            return processList.Take(processCount).ToArray();      }  

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