C++ Linker error undefined reference [duplicate] - c++

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Combining C++ and C - how does #ifdef __cplusplus work?
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What is an undefined reference/unresolved external symbol error and how do I fix it?
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Closed 4 years ago.
I have been working with C on the embedded side and C# on PC side for quite some time. Now I decided to start working with C++ on an embedded target.
However the linker tells me that it could not find my function.
The complete error looks like this:
Building target: Cpp_Test.elf
Invoking: MCU G++ Linker
arm-none-eabi-g++ -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 -specs=nosys.specs -specs=nano.specs -T"../STM32F429ZITx_FLASH.ld" -Wl,-Map=output.map -Wl,--gc-sections -fno-exceptions -fno-rtti -o "Cpp_Test.elf" #"objects.list" -lm
Src/freertos.o: In function `StartDefaultTask':
\Cpp_Test\Debug/../Src/freertos.c:127: undefined reference to `calc_values'
The test_cplus.h file looks like this:
#include "stdint.h"
int calc_values();
The test_cplus.cpp file looks like this:
#include "test_cplus.h"
#include <iostream>
using namespace std;
class Rectangle {
int width, height;
public:
void set_values (int,int);
int area() {return width*height;}
};
void Rectangle::set_values (int x, int y) {
width = x;
height = y;
}
int calc_values()
{
Rectangle rect;
rect.set_values(1,2);
int area = rect.area();
return area;
}
Could you point me in the right direction?
Edit freertos.c
/* Includes ------------------------------------------------------------------*/
#include "FreeRTOS.h"
#include "task.h"
#include "cmsis_os.h"
/* USER CODE BEGIN Includes */
#include "test_file.h"
#include "test_cplus.h"
/* USER CODE END Includes */
/* Variables -----------------------------------------------------------------*/
osThreadId defaultTaskHandle;
/* USER CODE BEGIN Variables */
/* USER CODE END Variables */
/* Function prototypes -------------------------------------------------------*/
#ifdef __cplusplus
extern "C" {
#endif
void StartDefaultTask(void const * argument);
extern void MX_USB_DEVICE_Init(void);
extern void MX_FATFS_Init(void);
void MX_FREERTOS_Init(void); /* (MISRA C 2004 rule 8.1) */
#ifdef __cplusplus
}
#endif
/* USER CODE BEGIN FunctionPrototypes */
/* USER CODE END FunctionPrototypes */
/* Hook prototypes */
/* Init FreeRTOS */
void MX_FREERTOS_Init(void) {
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* USER CODE BEGIN RTOS_MUTEX */
/* add mutexes, ... */
/* USER CODE END RTOS_MUTEX */
/* USER CODE BEGIN RTOS_SEMAPHORES */
/* add semaphores, ... */
/* USER CODE END RTOS_SEMAPHORES */
/* USER CODE BEGIN RTOS_TIMERS */
/* start timers, add new ones, ... */
/* USER CODE END RTOS_TIMERS */
/* Create the thread(s) */
/* definition and creation of defaultTask */
osThreadDef(defaultTask, StartDefaultTask, osPriorityNormal, 0, 128);
defaultTaskHandle = osThreadCreate(osThread(defaultTask), NULL);
/* USER CODE BEGIN RTOS_THREADS */
/* add threads, ... */
/* USER CODE END RTOS_THREADS */
/* USER CODE BEGIN RTOS_QUEUES */
/* add queues, ... */
/* USER CODE END RTOS_QUEUES */
}
/* StartDefaultTask function */
void StartDefaultTask(void const * argument)
{
/* init code for USB_DEVICE */
MX_USB_DEVICE_Init();
/* init code for FATFS */
MX_FATFS_Init();
/* USER CODE BEGIN StartDefaultTask */
/* Infinite loop */
for(;;)
{
run_test();
calc_values();
osDelay(100);
}
/* USER CODE END StartDefaultTask */
}
/* USER CODE BEGIN Application */
/* USER CODE END Application */