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I am trying to figure out .net and got this code that when I try to run from VS 2008 it gives me this error

A project with an Output Type of Class Library cannot be started directly.
In order to debug this project, add an executable project to this solution which references to the library project. Set the executable project as the startup project

I am learning C# so have no idea what to do here

user400749
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  • Possible duplicate of ["A project with an Output type of Class Library cannot be started directly"](https://stackoverflow.com/questions/3363106/a-project-with-an-output-type-of-class-library-cannot-be-started-directly) – kenorb Sep 18 '18 at 16:16

5 Answers5

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You cannot run a library. You could only run an executable or a web site. So right click on the corresponding project and Set as StartUp Project. Then you can run it:

enter image description here

Darin Dimitrov
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  • I dont understand it. You cannot have multiple solutions in your "Solution explorer". When I open program.sln, it opens in new window, then I open library.sln, it opens in new window too... In my library window, I cannot see Program solution ... In program window, when I set program solution as startup project, it doesnt affect library window – Buksy Feb 17 '13 at 22:21
  • Old question, helped me today, had swapped hard drives and somehow vsstudio forgot about this : ' ) – edencorbin Sep 11 '17 at 16:48
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A class library is, simply put, an assembly that exposes functionality that can be used by other assemblies, but it cannot be executed on its own. It needs some sort of consumer to make sense. This consumer can be one of many things, such as:

  • An asp.net web application
  • A windows application (WPF or winforms)
  • A console application

If you are not interested in developing a client application but just the class library, you typically use a unit testing framework which can invoke methods in the class library for testing purposes.

Fredrik Mörk
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You need to have a project that is runnable in order to use this assembly. If you add a project of type "Console Application" or "Windows Forms Application", you can use this assembly as a reference and use your code.

Is there more than one project in your solution? If so, (and if one of them are of a runnable type), you can right-click on one of them and set as startup project to be able to begin debugging.

Mark Avenius
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In your solution explorer right click on your web or forms project and hit set as startup project.

Your trying to launch a class library (which is not possible)

jonezy
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You selected the wrong project type. You might want an ASP.NET project, WinForms project, WPF project, Silverlight project or console project instead.

Daniel A. White
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    This might not be the wrong type of project, but @user is incorrectly trying to invoke it. We don't know the user's needs in this case. – Mark Avenius Feb 23 '11 at 19:23