Using STM32CubeMX generate code for STM32CubeIDE and than change main.c to main.cpp, and build project will show up undefined reference to 'main' error.

[jcRuan]

The error message like as:

Core/Startup/startup_stm32f765vitx.o: In function `LoopFillZerobss':

J:/STM32PRJ/CB_ENV/MS220_F765VI/VIDEOBOARD_V9A/20200520/Debug/../Core/Startup/startup_stm32f765vitx.s:97: undefined reference to `main'

​

collect2.exe: error: ld returned 1 exit status

make: *** [makefile:47: VideoBoard.elf] Error 1

"make -j8 all" terminated with exit code 2. Build might be incomplete.

​

How can I solve this problem?

[alister]

Explained https://www.geeksforgeeks.org/extern-c-in-c/ and many other places.

The LoopFillZerobss was indented to call a "C" main. Declare main like this in main.c before you define it, i.e. before the main() function.

extern "C"
{ 
 int main(void); 
} 

[jcRuan]

Hi @alister​ 

Thanks your replay.

I try to put extern "c" before the main() function but it doesn't work, the error message is the same. the code snippet following:

extern "C"
{
	int main(void)
	{
	 /* USER CODE BEGIN 1 */
 
	 /* USER CODE END 1 */
	
	 /* MCU Configuration--------------------------------------------------------*/
	
	 /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
	 HAL_Init();
	
	 /* USER CODE BEGIN Init */
	
	 /* USER CODE END Init */
	
	 /* Configure the system clock */
	 SystemClock_Config();
	
	 /* USER CODE BEGIN SysInit */
	
	 /* USER CODE END SysInit */
	
	 /* Initialize all configured peripherals */
	 MX_GPIO_Init();
	 MX_I2C3_Init();
	 MX_SPI3_Init();
	 MX_TIM6_Init();
	 /* USER CODE BEGIN 2 */
	 //sys_main->SysMainInit();//this is cpp function
	 /* USER CODE END 2 */
	
	 /* Infinite loop */
	 /* USER CODE BEGIN WHILE */
	 while (1)
	 {
		 //sys_main->SysMainLoop();//this is cpp function
		/* USER CODE END WHILE */
	
		/* USER CODE BEGIN 3 */
	 }
	 /* USER CODE END 3 */
	}
}

Do I need to modify the compilation settings?

[alister]

I'm guessing, try declaring it only as extern "C", not defining it.

Is there a main with a C++ mangled name in the linker map file, or what does main look like there?

Are you sure you're compiling/linking the file main's in?

Check https://stackoverflow.com/questions/18137814/loopfillzerobss-has-an-undefined-reference-to-main too.