Why is the console window closing immediately once displayed my output?

问题

I\'m studying C# by following the guides in MSDN.

Now, I just tried the Example 1 (here is the link to MSDN), and I\'ve encountered an issue: why is the console window closing immediately once displayed my output?

using System;

public class Hello1
{
    public static int Main()
    {
        Console.WriteLine(\"Hello, World!\");
        return 0;
    }
}

回答1:

the issue here is that their Hello World Program is showing up then it would immediately close.
why is that?

Because it's finished. When console applications have completed executing and return from their main method, the associated console window automatically closes. This is expected behavior.

If you want to keep it open for debugging purposes, you'll need to instruct the computer to wait for a key press before ending the app and closing the window.

The Console.ReadLine method is one way of doing that. Adding this line to the end of your code (just before the return statement) will cause the application to wait for you to press a key before exiting.

Alternatively, you could start the application without the debugger attached by pressing Ctrl+F5 from within the Visual Studio environment, but this has the obvious disadvantage of preventing you from using the debugging features, which you probably want at your disposal when writing an application.

The best compromise is probably to call the Console.ReadLine method only when debugging the application by wrapping it in a preprocessor directive. Something like:

#if DEBUG
    Console.WriteLine("Press enter to close...");
    Console.ReadLine();
#endif

You might also want the window to stay open if an uncaught exception was thrown. To do that you can put the Console.ReadLine(); in a finally block:

#if DEBUG
    try
    {
        //...
    }
    finally
    {
        Console.WriteLine("Press enter to close...");
        Console.ReadLine();
    }
#endif

回答2:

Instead of using

Console.Readline()
Console.Read()
Console.ReadKey()

you can run your program using Ctrl+F5 (if you are in Visual Studio). Then Visual Studio will keep the console window open, until you press a key.

Note: You cannot debug your code in this approach.

回答3:

This behaves the same for CtrlF5 or F5. Place immediately before end of Main method.

using System.Diagnostics;

private static void Main(string[] args) {

  DoWork();

  if (Debugger.IsAttached) {
    Console.WriteLine("Press any key to continue . . .");
    Console.ReadLine();
  }
}

回答4:

I assume the reason you don't want it to close in Debug mode, is because you want to look at the values of variables etc. So it's probably best to just insert a break-point on the closing "}" of the main function. If you don't need to debug, then Ctrl-F5 is the best option.

回答5:

The program immediately closes because there's nothing stopping it from closing. Insert a breakpoint at return 0; or add Console.Read(); before return 0; to prevent the program from closing.

回答6:

Alternatively, you can delay the closing using the following code:

System.Threading.Thread.Sleep(1000);

Note the Sleep is using milliseconds.

回答7:

Another way is to use Debugger.Break() before returning from Main method

回答8:

I'm a little bit late to the party, but: in Visual Studio 2019 for .NET Core projects the console doesn't close automatically by default. You can configure the behaviour through menu Tools → Options → Debugging → General → Automatically close the console when debugging stops. If you get your console window automatically closing, check if the mentioned setting is not set.

The same applies to the .NET Framework new style console projects:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net472</TargetFramework>
  </PropertyGroup>

</Project>

The old style .NET Framework project still unconditionally close the console at the end (as of Visual Studio 16.0.1).

Reference: https://devblogs.microsoft.com/dotnet/net-core-tooling-update-for-visual-studio-2019-preview-2/

回答9:

If you want to keep your application opened, you have to do something in order to keep its process alive. The below example is the simplest one, to be put at the end of your program:

while (true) ;

However, it'll cause the CPU to overload, as it's therefore forced to iterate infinitely.

At this point, you can opt to use System.Windows.Forms.Application class (but it requires you to add System.Windows.Forms reference):

Application.Run();

This doesn't leak CPU and works successfully.

In order to avoid to add System.Windows.Forms reference, you can use a simple trick, the so-called spin waiting, importing System.Threading:

SpinWait.SpinUntil(() => false);

This also works perfectly, and it basically consists of a while loop with a negated condition that is returned by the above lambda method. Why isn't this overloading CPU? You can look at the source code here; anyway, it basically waits some CPU cycle before iterating over.

You can also create a message looper, which peeks the pending messages from the system and processes each of them before passing to the next iteration, as follows:

[DebuggerHidden, DebuggerStepperBoundary, DebuggerNonUserCode, DllImport("user32.dll", EntryPoint = "PeekMessage")]
public static extern int PeekMessage(out NativeMessage lpMsg, IntPtr hWnd, int wMsgFilterMin, int wMsgFilterMax, int wRemoveMsg);

[DebuggerHidden, DebuggerStepperBoundary, DebuggerNonUserCode, DllImport("user32.dll", EntryPoint = "GetMessage")]
public static extern int GetMessage(out NativeMessage lpMsg, IntPtr hWnd, int wMsgFilterMin, int wMsgFilterMax);

[DebuggerHidden, DebuggerStepperBoundary, DebuggerNonUserCode, DllImport("user32.dll", EntryPoint = "TranslateMessage")]
public static extern int TranslateMessage(ref NativeMessage lpMsg);

[DebuggerHidden, DebuggerStepperBoundary, DebuggerNonUserCode, DllImport("user32.dll", EntryPoint = "DispatchMessage")]
public static extern int DispatchMessage(ref NativeMessage lpMsg);

[DebuggerHidden, DebuggerStepperBoundary, DebuggerNonUserCode]
public static bool ProcessMessageOnce()
{
    NativeMessage message = new NativeMessage();

    if (!IsMessagePending(out message))
        return true;

    if (GetMessage(out message, IntPtr.Zero, 0, 0) == -1)
        return true;

    Message frameworkMessage = new Message()
    {
        HWnd = message.handle,
        LParam = message.lParam,
        WParam = message.wParam,
        Msg = (int)message.msg
    };

    if (Application.FilterMessage(ref frameworkMessage))
        return true;

    TranslateMessage(ref message);
    DispatchMessage(ref message);

    return false;
}

Then, you can loop safely by doing something like this:

while (true)
    ProcessMessageOnce();

Even, you could mix the latter two solutions, replacing the while loop with a SpinWait.SpinUntil call:

SpinWait.SpinUntil(ProcessMessageOnce);

回答10:

The code is finished, to continue you need to add this:

Console.ReadLine();

or

Console.Read();

回答11:

Use Console.Read(); to prevent the program from closing, but make sure you add the Console.Read(); code before return statement, or else it will be a unreachable code .

    Console.Read(); 
    return 0; 

check this Console.Read

回答12:

Add The Read method to show the output.

Console.WriteLine("Hello, World!");
Console.Read();
return 0;

回答13:

Here is a way to do it without involving Console:

var endlessTask = new TaskCompletionSource<bool>().Task;
endlessTask.Wait();

回答14:

The program is closing as soon as it's execution is complete. In this case when you return 0;. This is expected functionality. If you want to see the output then either run it in a terminal manually or set a wait at the end of the program so that it will stay open for a few seconds ( using the threading library ).

回答15:

this is the answer async at console app in C#?

anything whereever in the console app never use await but instead use theAsyncMethod().GetAwaiter().GetResult();,

example

var result = await HttpClientInstance.SendAsync(message);

becomes

var result = HttpClientInstance.SendAsync(message).GetAwaiter().GetResult();

回答16:

if your program requires you to press enter to continue like you have to enter a value and continue, then add a new double or int and type write before retunr(0); scanf_s("%lf",&the variable);

回答17:

I always add the following statement to a console application.(Create a code snippet for this if you wish)

Console.WriteLine("Press any key to quit!");
Console.ReadKey();

Doing this helps when you want to experiment different concepts through console application.

Ctr + F5 will make the Console stay but you cant debug! All the console applications that I have written in realworld is always non-interactive and triggered by a Scheduler such as TWS or CA Work station and did not require something like this.

回答18:

To simplify what others are saying: Use Console.ReadKey();.

This makes it so the program is waiting on the user to press a normal key on the keyboard

Source: I use it in my programs for console applications.

回答19:

You can solve it very simple way just invoking the input. However, if you press Enter then the console will disapper again. Simply use this Console.ReadLine(); or Console.Read();

回答20:

Add the following before the return 0:

system("PAUSE");  

This prints a line to hit a key to close the window. It will keep the window up until you hit the enter key. I have my students add it to all their programs.

回答21:

According to my concern, if we want to stable the OUTPUT OF CONSOLE APPLICATION, till the close of output display USE, the label: after the MainMethod, and goto label; before end of the program

In the Program.

eg:

static void Main(string[] args)
{
    label:

    // Snippet of code

    goto label;
}

来源：https://stackoverflow.com/questions/8868338/why-is-the-console-window-closing-immediately-once-displayed-my-output