STM32 printf function remapping

#ifdef __GNUC__
  /* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf
     set to 'Yes') calls __io_putchar() */
  #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
  #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */

/**
  * @brief Retargets the C library printf function to the USART.
  * @param None
  * @retval None
  */
PUTCHAR_PROTOTYPE
{
  /* Place your implementation of fputc here */
  /* Loop until the end of transmission */
  while ( USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TC) == RESET)
  {}
  
  /* write a character to the USART */
  USART_SendData(EVAL_COM1, (uint8_t) ch);

  return ch;
}

Someone's explanation:

This code means redirecting or remapping the C language library function printf. This term is a bit too professional. To put it simply,
the printf function in the C language library will call the hardware interface function PUTCHAR_PROTOTYPE to output a char type variable to the display for display.
Of course, STM32 does not have a display, so it uses UART to output a char type variable to the PC, which is displayed by the PC's hyperterminal. To put it bluntly,
the display data originally sent to the monitor is now sent to the STM32 serial port.
If it cannot be transferred, you need to pay attention to two points:
1. Is your board using USART1? If so, then connect it to the PC's serial port and you can see the printed content on the hyperterminal. If not, please refer to point 2.
2. Initialize the USART on your board first, and then replace the USART1 in the PUTCHAR_PROTOTYPE function body with the USART you are using now. Here is
a note for free, of course, the above are also free, haha
​​1. The peripheral output pins of STM32 can be remapped, such as USART2. Pay attention to whether the board is connected according to the original pins or remapped. If it is remapped, please refer to point 2.
2. If the connection is a remapped pin, please add a remapping function before the original initialization. Of course, there is also this part of code in the ST routine, which can be referred to.