Author: Abhay Kant

Printf() function can be redirected to USART and also towards SWO.

Here you will see how to redirect printf() to USART in STM32f103RB

You need to rewrite this code in your main.c file

/*
* Function Name: _write
* Function Description: Redirect the printf() statement towards the UART using the HAL_UART_Transmit
Author: Abhay

*/
int _write(int fd, char* ptr, int len) {
    HAL_UART_Transmit(&huart1, (uint8_t *) ptr, len, HAL_MAX_DELAY);
    return len;
}

If you have created your project using STM32CubeMX or STM32 Cube IDE, then you can rewrite it in between USER CODE BEGIN 0 as shown

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
int _write(int fd, char* ptr, int len) {
    HAL_UART_Transmit(&huart1, (uint8_t *) ptr, len, HAL_MAX_DELAY);
    return len;
}
/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
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_USART1_UART_Init();
  /* USER CODE BEGIN 2 */
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */

  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */

  }
  /* USER CODE END 3 */
}

After adding the code, connect the uart to your laptop or computer using serial to USB adapter and open serial Terminal application like YAT.
Then you will be able to see printf message over there.