/* Private variables ---------------------------------------------------------*/

/* USER CODE BEGIN PV */

char ext0;

/* USER CODE END PV */


and it is used as the external variable inside the stm32f7xx_it.c as follows :


/* External variables --------------------------------------------------------*/


/* USER CODE BEGIN EV */

extern char ex0;

void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin) {
    if ( GPIO_Pin == GPIO_PIN_13 ) {
        ex0 = 1;
    }
}

/* USER CODE END EV */