从源字符串中截取指定长度的字符串改变截取的位置查看串口输出小数保留有效位是截取字符串的一种特例Serial115200Serialprintlnsubstring03Serialprintln6.6662dm9pZCBzZXR1cCgpewogIFNlcmlhbC5iZWdpbigxMTUyMDApOwogIFNlcmlhbC5wcmludGxuKFN0cmluZygic3Vic3RyaW5nIikuc3Vic3RyaW5nKDAsMykpOwogIFNlcmlhbC5wcmludGxuKFN0cmluZyg2LjY2NiwgMikpOwp9Cgp2b2lkIGxvb3AoKXsKICAvL+S7jua6kOWtl+espuS4suS4reaIquWPluaMh+WumumVv+W6pueahOWtl+espuS4sgogIC8v5pS55Y+Y5oiq5Y+W55qE5L2N572u5p+l55yL5Liy5Y+j6L6T5Ye6CiAgLy/lsI/mlbDkv53nlZnmnInmlYjkvY3mmK/miKrlj5blrZfnrKbkuLLnmoTkuIDnp43nibnkvosKCn0=