How to detect and convert Punycode in url?

Question

C++ / C#

There are many different url addresses, they also contain Cyrillic host names.
How to understand that a given URL has a host in Punycode, so that later it can be decrypted from Punycode using System.Globalization.IdnMapping?

Answer 1

Domain names in punycode begin with "xn--"
And each segment is separate, including zero.