Very strong -- I've been using C++ professionally for over two decades. I can tell you about std::optional and string_view, explain the one-definition rule, and know what std::move actually does. I can write an overload and an override. I've crashed std::sort and I've signal-handled a segfault. I can even fake my way through an explanation of memory_order_relaxed vs. memory_order_acquire/memory_order_release vs. memory_order_seq_cst.

But I haven't had much chance to play with templates after the C++11 improvements, so I wanted to work on that.