Making Sense of Common C# Compiler Errors

Matt Eland
19 min readOct 26, 2021
Photo by Elisa Ventur on Unsplash

I get to help a lot of people learn C# programming every year. As I watch new developers grow and get used to working in C# and Visual Studio, it has become fairly clear to me that reading C# compiler errors and even their documentation is an acquired skill. I’ve made a request for Microsoft to improve the error message feedback in Visual Studio, but until that’s resolved developers still have a tough time working through early obstacles.

Because of this, I’m creating this unusual post to serve as beginner-friendly documentation to what I personally view as the most likely compiler errors a new developer is likely to encounter. Microsoft has wonderful documentation on compiler errors, and this is something that will help you out significantly as you grow, but early on a paragraph or two aimed at a beginner can be exactly what you need.

I also snuck in a few of the more interesting compiler errors I noticed about the maximum limits of the C# compiler, so even if you’re very familiar with C# at this point you’ll likely still learn a few things skimming this list.

Take a look at my list and my recommendations on these issues and let me know if you find this helpful or encounter something I missed.

CS0003 — Out of Memory

This occurs when a computer runs out of memory compiling your code. Close any unnecessary programs and reboot the machine if the problem persists.

CS0004 — Warning Treated as Error

Developers may configure projects to treat certain warnings as errors. These warnings may be specified in the build section of the project’s properties. Typically it is best to resolve the specific warning listed in the build errors since someone wanted that to be treated severely.

CS0015 — Type Name too Long

.NET requires the names of types and namespaces to be less than 1024 characters. If you find yourself getting this error, you may want to reconsider your team’s naming choices.

CS0017 — More than one entry point defined

This occurs when your program has more than one class defined with a static void main method. Remove one…

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Matt Eland

Microsoft MVP in AI, AI Specialist at Leading EDJE. Author of "Refactoring with C#".