在“usart.c”文件中加入以下代码

#ifdef __GNUC__

       #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else

       #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif

PUTCHAR_PROTOTYPE

{
              HAL_UART_Transmit(&huart1 , (uint8_t *)&ch, 1, 0xFFFF);
              return ch;
}