How do I attach Visual Studio to a process that is not started yet?

Question

I have .NET program that can\'t be run from Visual Studio for some reasons (Excel file created from an Excel 2010 template project) for which I need to debug startup events.

Answer 1

You can start the debugger from your code via

public static void Main(string[] args)
{
  System.Diagnostics.Debugger.Launch();
}

But don't for get to remove this line before shipping your application. Maybe you want to use compiler flags to be sure:

    public static void Main(string[] args)
    {
      #if debug
      System.Diagnostics.Debugger.Launch();
      #endif
    }

Answer 2

I was debugging a C++ plugin in an externally spawned process that crashed by throwing an exception at startup and this worked perfectly for me:

Add the free Reattach Extension for Visual Studio. Ask it to reattach to the process name before it is launched. It will pop a modal dialog saying it is waiting for the process name to launch.

Now launch the process and the Visual Studio debugger will attach immediately, catching exceptions and hitting breakpoints.

Answer 3

Actually you can; you don't attach to it, you start it. On the properties of your project, on the Debugging tab, specify the path of the program you want to attach to in the "Command" textbox.

You can also enter any command-line arguments for the program in the "Command Arguments" box:

Ensure that "Attach" is set to "No".

Answer 4

If there's no process then Visual Studio can't attach to it.

However, you can set the startup program of your project to be something other than the output of your project.

Answer 5

Follow these steps if you have Visual Studio 2017-2019:

1. File > Open > Project/Solution
2. Choose your .exe
3. Debug > Start Debugging

Much easier than other suggestions: you don't have to mess with project properties, and no extensions are needed.

Answer 6

You can show a MessageBox, this would block the application, then you attach or reattach the debugger to the process and click ok to continue:

MessageBox.Show("Attach process to debugger and click ok!");

you can add it to the Form constructor (if you use winforms), so this would be executed before anything else, except for the initialization of components:

public MainForm()
{
    InitializeComponent();
    MessageBox.Show("Attach process to debugger and click ok!");
}

When you finish your debugging, comment out that line.