This is the complete error message:
In file included from /home/berni/Arduino/oled_mit_ds18b20/oled_mit_ds18b20.ino:3:0:
/home/berni/Arduino/libraries/Adafruit_SSD1306-master/Adafruit_SSD1306.h:49:26: fatal error: Adafruit_GFX.h: No such file or directory
#include <Adafruit_GFX.h>
I cannot understand the error on #include <Adafruit_GFX.h> because it is after //?
It shoul be a comment. The original code is from an example.