I have now solved this problem with Fahrenheit instead of Celcius.
I had to change to this --->
float temperature = static_cast<float>(static_cast<int>((dallasTemp.getTempCByIndex(i)) * 10.)) / 10.;
From this --->
float temperature = static_cast<float>(static_cast<int>((gw.getConfig().isMetric ? dallasTemp.getTempC(dallasAddresses[i]) : dallasTemp.getTempF(dallasAddresses[i])) * 10.)) / 10.;
Now it gives me celcius.
Thanks for nice example.