Redirect printf() to UART on STM32 microcontroller

STM32HAL_printf_uart.c

/* USER CODE BEGIN Includes */
#include <stdio.h>




/* USER CODE BEGIN 0 */

/* PRINTF REDIRECT to UART BEGIN */
// @see    http://www.keil.com/forum/60531/
// @see    https://stackoverflow.com/questions/45535126/stm32-printf-redirect

struct __FILE{
  int handle;
  /* Whatever you require here. If the only file you are using is */
  /* standard output using printf() for debugging, no file handling */
  /* is required. */
};

FILE __stdout;

int fputc(int ch, FILE *f){
	HAL_UART_Transmit(&huart3, (uint8_t *)&ch, 1, 0xFFFF);
  return ch;
}

int ferror(FILE *f){
  /* Your implementation of ferror(). */
  return 0;
}
/* PRINTF REDIRECT to UART END */

/* USER CODE END 0 */

How it is works?