重写fput函数 

#include <stdio.h>
 
 #ifdef __GNUC__
     #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
 {
     HAL_UART_Transmit(&huart1, (uint8_t *)&ch,1,0xFFFF);
     return ch;
 }