Need Example(s) for Reading-Writing Ariadne MAC address within my own sketch about ariadne-bootloader HOT 1 CLOSED

The MAC address is different that the IP address as the NetEEPROM.readMAC(); returns a pointer to an array allocated in the memory. The readIP();, readGW(); and readSN(); return an object of type IPAddress.

In C++, functions can return object instances, much like they can return any other type, such as int, float, double and so on. But just like C, they cannot return an array. Instead of that, they can return a pointer to an array.

So what happens in the case of the first three is: somewhere in your code, before the call of NetEEPROM.readIP();
you have declared a variable ip with type IPAddress which is the class used by Arduino to store IP addresses.
What happens when you do something like ip = NetEEPROM.readIP(); is that the NetEEPROM.readIP(); reads the IP address and returns an IPAddress object, which is then copied to the ip variable through the = operator.
After that you can manipulate it as any other object of this type.

In the case of the MAC address, there isn't such an object, so it returns a pointer to a byte array. So to 'read' the MAC address you have to do something like byte *mac = NetEEPROM.readMAC();. After that you can get the individual elements of the array with mac[0] to mac[5]. To give you an example, this is how the MAC is printed in NetEEPROM.printNet(&serial);:

    byte* mac = readMAC();
    serial->print("    MAC: ");
    for(uint8_t i = 0; i < 6; i++) {
        serial->print("0x");
        serial->print(mac[i], HEX);
        if(i != 5) serial->print(".");
        else serial->println();
    }
    free(mac);

One more thing to notice is the free(mac); line. In the readMAC(); the array is being allocated in the memory, and it is not automatically freed. So after doing whatever you want with the MAC address, you should free it, otherwise, you will end up with all of the Arduino memory polluted with MAC arrays.

from ariadne-bootloader.