Question on C# version on VS Projects

I have recently inherited a Visual Studio 2022 project, it is a C# Console application on .Net Framework 4.8. So I thought not a very old project what can go wrong.

Well, when I worked on the project, only into first few hours, I have faced following error:

Feature 'nullable reference types' is not available in C# 7.3. Please use language version 8.0 or greater.

I got this error because I tried to use Nullable type in my new code I was developing. But I was thinking, why would this project is using C# 7.3? At the time of writing latest version of the C# was version 13, which was released with .NET 9.0 in 2024. So how come C# version used in relatively new project has taken version 7.3?

To find the answer I have turned to ChatGPT and web. This is what it had to tell:

The default version of the C# depends on the the target framework of your project. Here is the default versions for .NET Framework 4.6.2 and 4.8:

.NET Framework Version	Default C# Version	Maximum Supported Version
.Net Framework 4.6.2	C# 7.0	C# 7.3
.Net Framework 4.8	C# 7.3	Latest version as of now

That explained lot. This project was created on .Net Framework 4.8, so it has defaulted to C# version 7.3.

Next question pop-up to me was, then how can I upgrade C# version on this project to more latest version, so I can use new features in the language in my code?

Answer is, you need to manually edit the .csproj file (i.e. Visual Studio project file). You need to insert something similar to below:

<PropertyGroup>

  <LangVersion>8.0</LangVersion>

</PropertyGroup>

If you want to use latest version of the language forever, you can do following:

<PropertyGroup>

  <LangVersion>latest</LangVersion>

</PropertyGroup>

However one of the thing to consider is, although .Net Framework 4.8 support latest version of the language, some of the features require runtime support which is only available in Framework. For example async streams, interface methods require runtime support of .Net Core/.NET 5+.

Unfortunately, there is no setting to tell on Visual Studio project to tell, which version of C# language in use. So if your csproj file doesn't have above property, you need to infer that your project will use the default version of the Framework as the language version.

If you are using more modern Frameworks, here are the default C# versions go with them:

• .NET 8 => default to C# 12
• .NET 7 => default to C# 11
• .NET 6 => default to C# 10