在单片机中使用类似printf函数在串口进行打印。

函数参数的传递原理
　　函数参数是以数据结构:栈的形式存取,从右至左入栈。

VOID Nguhyw_printf(const char *fmt, ...)
{
    va_list args;
    int length;
    char log_buf[CFG_CONSOLEBUF_SIZE];

    va_start(args, fmt);
    /* the return value of vsnprintf is the number of bytes that would be
     * written to buffer had if the size of the buffer been sufficiently
     * large excluding the terminating null byte. If the output string
     * would be larger than the log_buf, we have to adjust the output
     * length. */
    length = vsnprintf(log_buf, sizeof(log_buf) - 1, fmt, args);
    if (length > CFG_CONSOLEBUF_SIZE - 1)
        length = CFG_CONSOLEBUF_SIZE - 1;

    uart_write(log_buf, length);
    va_end(args);
}