STM32重定义printf，实现串口打印

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