C++ regex need to match names containing diacritics

I need to match two word names like (Johny Cash). So I was using the regex:

L"^[A-Z][a-z]+\\s+[A-Z][a-z]+$"

However, I realized that the names may contain diacritics as well, something like Johannes Fürnkranz. I came across this solution: https://stackoverflow.com/a/8923865/1469954, and modified my regex to:

L"^[A-Z].\\p{L}+\\s+[A-Z].\\p{L}+$

This, assuming that the first letter in each word won't be a diacritic. However, I am getting an invalid regex error. Any idea how to make it work?