Compiling error - undefined reference to 'main'

Projects Programming
1

Hi, I read many posts about this already, but none seemed to apply to my case.
I am trying to compile the project 2 from the Arduino Projects book.

const int sensorPin = A0;
const float baselineTemp = 20.0;

void setup() {
  Serial.begin(9600);

  for (int pinNumber = 2; pinNumber < 5; pinNumber++) {
    pinMode(pinNumber, OUTPUT);
    digitalWrite(pinNumber, LOW);
  }
}

void loop() {
  int sensorVal = analogRead(sensorPin);

  Serial.print("Sensor value:");
  Serial.print(sensorVal);

  float voltage = (sensorVal / 1024.0) * 5.0;
  Serial.print(", Volts:");
  Serial.print(voltage);

  float temperature = (voltage - .5) * 100;
  Serial.print(", Temperature in C:");
  Serial.println(temperature);

  if (temperature < baselineTemp) {
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
  } else if (temperature >= baselineTemp + 2 && temperature < baselineTemp + 4) {
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
  } else if (temperature >= baselineTemp + 4 && temperature < baselineTemp + 6) {
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, LOW);
  } else if (temperature > baselineTemp + 6) {
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);
  }
  delay(1);
}

When I click Verify, the following is printed (I activated Verbose mode):

C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\arduino-builder -dump-prefs -logger=machine -hardware C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware -hardware C:\Users\gmussi\Documents\ArduinoData\packages -tools C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\tools-builder -tools C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -tools C:\Users\gmussi\Documents\ArduinoData\packages -built-in-libraries C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\libraries -libraries C:\Users\gmussi\Documents\Arduino\libraries -fqbn=arduino:avr:uno -vid-pid=0X2A03_0X0043 -ide-version=10802 -build-path C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867 -warnings=none -build-cache C:\Users\gmussi\AppData\Local\Temp\arduino_cache_927296 -prefs=build.warn_data_percentage=75 -prefs=runtime.tools.arduinoOTA.path=C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -prefs=runtime.tools.avr-gcc.path=C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -prefs=runtime.tools.avrdude.path=C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -verbose C:\Users\gmussi\Documents\Arduino\sketch_may14c\sketch_may14c.ino
C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\arduino-builder -compile -logger=machine -hardware C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware -hardware C:\Users\gmussi\Documents\ArduinoData\packages -tools C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\tools-builder -tools C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -tools C:\Users\gmussi\Documents\ArduinoData\packages -built-in-libraries C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\libraries -libraries C:\Users\gmussi\Documents\Arduino\libraries -fqbn=arduino:avr:uno -vid-pid=0X2A03_0X0043 -ide-version=10802 -build-path C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867 -warnings=none -build-cache C:\Users\gmussi\AppData\Local\Temp\arduino_cache_927296 -prefs=build.warn_data_percentage=75 -prefs=runtime.tools.arduinoOTA.path=C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -prefs=runtime.tools.avr-gcc.path=C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -prefs=runtime.tools.avrdude.path=C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr -verbose C:\Users\gmussi\Documents\Arduino\sketch_may14c\sketch_may14c.ino
Using board 'uno' from platform in folder: C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr
Using core 'arduino' from platform in folder: C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr
Detecting libraries used...
"C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr/bin/avr-g++" -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics  -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10802 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR   "-IC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr\cores\arduino" "-IC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr\variants\standard" "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\sketch\sketch_may14c.ino.cpp" -o "nul"
Generating function prototypes...
"C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr/bin/avr-g++" -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics  -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10802 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR   "-IC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr\cores\arduino" "-IC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr\variants\standard" "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\sketch\sketch_may14c.ino.cpp" -o "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\preproc\ctags_target_for_gcc_minus_e.cpp"
"C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\tools-builder\ctags\5.8-arduino11/ctags" -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\preproc\ctags_target_for_gcc_minus_e.cpp"
Compiling sketch...
"C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr/bin/avr-g++" -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10802 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR   "-IC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr\cores\arduino" "-IC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\arduino\avr\variants\standard" "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\sketch\sketch_may14c.ino.cpp" -o "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\sketch\sketch_may14c.ino.cpp.o"
Compiling libraries...
Compiling core...
Using precompiled core
Linking everything together...
"C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.3.0_x64__mdqgnx93n4wtt\hardware\tools\avr/bin/avr-gcc" -w -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections -mmcu=atmega328p  -o "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867/sketch_may14c.ino.elf" "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867\sketch\sketch_may14c.ino.cpp.o" "C:\Users\gmussi\AppData\Local\Temp\arduino_build_676867/..\arduino_cache_927296\core\core_arduino_avr_uno_9b2c1f9a62e2088809b965d307a2a6e8.a" "-LC:\Users\gmussi\AppData\Local\Temp\arduino_build_676867" -lm
c:/program files/windowsapps/arduinollc.arduinoide_1.8.3.0_x64__mdqgnx93n4wtt/hardware/tools/avr/bin/../lib/gcc/avr/4.9.2/../../../../avr/lib/avr5/crtatmega328p.o:(.init9+0x0): undefined reference to `main'

collect2.exe: error: ld returned 1 exit status

exit status 1
Error compiling for board Arduino/Genuino Uno.

I am running the Arduino IDE 1.8.2 on a Windows 10 computer.
My Java is also the latest version.

How do I debug such problems?

2

When I tried to run the sketch with just a stud loop and setup, it still gave the same error message.

When I copied the code above, and pasted into a NEW sketch, then it compiled and uploaded without problems.

What went wrong? I am trying to understand how this works. I work with Java and am trying to learn to work with hardware / arduino.

3

No idea what went wrong. But any C/C++ program starts with a function called main. And for some reason, it could not be found.

Might have been a glitch in the IDE that tries to do some fancy processing before calling the compiler.

4

When I compile your code, for a Duemilanove, I get:

Sketch uses 4078 bytes (13%) of program storage space. Maximum is 30720 bytes.
Global variables use 240 bytes (11%) of dynamic memory, leaving 1808 bytes for local variables. Maximum is 2048 bytes.

Uninstall and reinstall the IDE.