WiFi.localIP() to string

localIP2str

char buf[16];
sprintf(buf, "IP:%d.%d.%d.%d", WiFi.localIP()[0], WiFi.localIP()[1], WiFi.localIP()[2], WiFi.localIP()[3] );

IPAddress ip = WiFi.localIP();
sprintf(lcdBuffer, "%d.%d.%d.%d:%d", ip[0], ip[1], ip[2], ip[3], udpPort);

Thanks. You can also use inbulilt .toString() funciton. Example usage:
server.send(200, "text/plain", "Please go to : " + WiFi.localIP().toString() + "/test");

Then how to reverse that？

a simple snippet in some function:

String ip2Str(IPAddress ip){
  String s="";
  for (int i=0; i<4; i++) {
    s += i  ? "." + String(ip[i]) : String(ip[i]);
  }
  return s;
}

good luck!

But, then how to pass/assign "s" to be used as a String in other parts of the code.