How to Debug a C# Class Library Project That Throws a 'Cannot Be Started Directly' Error?

Debugging a Class Library Project: Overcoming the "Cannot Be Started Directly" Error

While attempting to debug a downloaded C# project, you may encounter the following error message: "A project with an Output type of Class Library cannot be started directly." This error indicates that the project you're trying to debug is intended to function as a reusable library and lacks an executable entry point such as a main function.

Understanding the Issue

A class library project comprises a collection of classes and functions that can be utilized by other applications. It does not possess an inherent entry point, unlike executable projects like console or windows applications. When you attempt to debug a class library project directly, Visual Studio prompts you to create an executable project that references the library and sets it as the startup project.

Solution:

To overcome this issue and debug your project effectively, follow these steps:

1. Add an Executable Project: Create a new project within the current solution using Visual Studio. Choose an executable project type such as Console Application or Windows Application.
2. Reference the Library Project: Add a reference to the class library project within your executable project. This will make your executable project aware of the classes and functionality contained in the library.
3. Set Executable Project as Startup: In the Solution Explorer, right-click on your executable project and select "Set as StartUp Project." This ensures that the executable project will be run when you start debugging.
4. Implement Test Logic: Within your executable project, implement code that utilizes the classes and functionality provided by the library project. This will allow you to test the library and debug any potential issues.

Additional Notes:

• You can modify the output type of a project by right-clicking on it in Solution Explorer and selecting "Properties." Navigate to the "Application" tab and locate the "Output type" drop-down menu.
• Class library projects are often distributed as NuGet packages for easy installation and consumption in other applications.

By following these steps, you can effectively debug class library projects and verify their functionality within the context of an executable application.

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