DII
DevHeads IoT Integration Server•5mo ago
Sterling

SWV printf Output Issue in C++ on STM32G431KB

I am currently utilizing an STM32G431KB board that differs from other boards in the STM32 Nucleo series as it has a wired SWO. While setting up SWV printf on a Nucleo variant of the same product, I encountered an inquiry and implemented suggestions given by its first answer which allowed me to enable functioning SWV under C programming language. However, upon switching over to C++, no output is visible during usage of this feature. For the C project, I created a new project, switched Debug to "Trace Asynchronous SW," and added the following code: 
/* USER CODE BEGIN Includes */
#include "stdio.h"
/* USER CODE END Includes */


/* USER CODE BEGIN 0 */
int _write(int file, char *ptr, int len)
{
    int DataIdx;
    for (DataIdx = 0; DataIdx < len; DataIdx++)
    {
        ITM_SendChar(*ptr++);
    }
    return len;
}
/* USER CODE END 0 */
/* USER CODE BEGIN Includes */
#include "stdio.h"
/* USER CODE END Includes */


/* USER CODE BEGIN 0 */
int _write(int file, char *ptr, int len)
{
    int DataIdx;
    for (DataIdx = 0; DataIdx < len; DataIdx++)
    {
        ITM_SendChar(*ptr++);
    }
    return len;
}
/* USER CODE END 0 */
In the main loop, I added: 
/* USER CODE BEGIN 2 */
int i = 0;
/* USER CODE END 2 */

/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
    printf("%d Hello World!\n", ++i);
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
/* USER CODE BEGIN 2 */
int i = 0;
/* USER CODE END 2 */

/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
    printf("%d Hello World!\n", ++i);
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
Upon activating SWV in the Debug Configuration, adjusting the core clock to 170 MHz, deactivating timestep in SWV settings and empowering port 0; executing C yields optimal results with expected output. On renaming main.c to main.cpp, the project operates in C++, but there is no result. What could be the reason for this problem?
2 Replies
Dark AI
Dark AI•5mo ago
hi, @Sterling the issue you're facing is likely due to name mangling in C++. You can fix this by declaring the _write function with extern "C", which makes sure the C standard library recognizes it correctly. This should get your SWV printf output working as expected
Sterling
Sterling•5mo ago
Thanks @Dark AI , I am gonna try using extern "C" to resolve the name mangling issue. Just to clarify, should I apply extern "C" to the _write function only, or are there other parts of the code that also need this adjustment in C++?

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