An answer two years too late, but your code returns the incorrect result when T is unsigned. The vs function is where the problem lies.

Well, this one is ancient, so it might be the reason

But it actually is very annoying that kata's difficulty has a very weak correlation with its actual level of difficulty

Free points, lol

Assert::That (sortTheInnerContent (input, strlen (input)), Equals (expected));

It looks like it's the length of the input string. Read the posts below, as I don't really do C++ but there are some posts about that already.

I have the same problem c++

No clue here either, but maybe you can find something useful in this article: https://docs.codewars.com/training/troubleshooting