Re: Feature request: "u" option to file:read
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- Subject: Re: Feature request: "u" option to file:read
- From: Dirk Laurie <dirk.laurie@...>
- Date: 2018年2月23日 18:00:02 +0200
2018年02月23日 16:46 GMT+02:00 Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br>:
>> "u": reads one or more bytes forming one UTF-8 character, and returns
>> that character as a string. Returns nil if the file at the current
>> position does not start with a valid UTF-8 sequence.
>
> Can this be done without having to unget more than one byte from the stream?
My rough workaround in Lua is this:
function readutf8(f)
local pos = f:seek()
local len = math.min(4,f:seek"end"-pos)
f:seek("set",pos)
local buf = f:read(len)
while utf8.len(buf)~=1 and #buf>1 do buf = buf:sub(1,-2) end
if utf8.len(buf)==1 then
f:seek("set",pos+#buf)
return buf
end
f:seek("set",pos)
end
This has only one unget, at the expense of always reading four bytes
except when the file is shorter.