Comment by pjmlp

Modern C# version,

    using var sr = new StreamReader(filename);

    txt = sr.ReadToEnd();

And for the "what about forgeting to call using?",

https://devblogs.microsoft.com/dotnet/infer-interprocedural-...

No different from using all those static analisers in C and C++ to keep the code free of memory corruptions and UB issues.