It turns out that constants aren’t only problematic in ASP .NET 5.

If you have a pretty long const string with a null character (\0) somewhere towards the beginning, then you’ll be pretty surprised to get the following error when you try to compile:

Unexpected error writing debug information — ‘Error HRESULT E_FAIL has been returned from a call to a COM component.’

Say you have a 3,000-character string that looks something like this:

const string s = "aaaaaaaaaaaa\0aa...aaaaa";

Although this is perfectly valid, Visual Studio fails to compile it:

I created a Stack Overflow question and a Visual Studio bug report for this.

Comments on the Stack Overflow question confirmed this to be a bug in the PDB writer (Eric Lippert). It’s Visual Studio specific, and doesn’t happen when compiling from the command line (Jon Skeet). Apparently it happens if the null character is before the 2033rd index in the string (Tommy).

One workaround suggested by Tommy is to use the string literal notation, which actually works:

const string s = @"aaaaaaaaaaaa\0aa...aaaaa";

Another workaround is to simply drop the const qualifier.