Thankyou Ibernstone, I appreciate the responce.
However, as I said I might as well be a C++ beginner and the header is not at all clear. I cannot see anywhere in your linked WiFiSTA.h that it hints that c_string() will be overloaded for macaddress in particular, or for all uint8_t. This is I suspect ...

I am just beginning with arduino, and am so rusty at C++ that I might as well be a beginner.

Including <WiFi.h> , then thanks to the arduino IDE suggestions I was able to guess that WiFi.macaddress().c_string() returned a ':' delimited string of the return type of WiFi.macaddress(), but I am not ...