Re: Most efficient way to recognize a line by its first (up to) three characters
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- Subject: Re: Most efficient way to recognize a line by its first (up to) three characters
- From: Sean Conner <sean@...>
- Date: 2014年3月11日 14:30:29 -0400
It was thus said that the Great meino.cramer@gmx.de once stated:
> Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br> [14-03-11 19:16]:
> > > local prefix, info = line:sub(1,3), line:sub(4)
> > > if prefix == "abc" then
> > > -- do something
> > > elseif prefix == "123" then
> > > -- do something else
> > > elseif ...
> >
> > Consider this scheme instead of a chain of ifs:
> >
> > local handlers={
> > ["abc"]=function (prefix,info) ... end,
> > ["123"]=function (prefix,info) ... end,
> > }
> >
> > local badprefix=function (prefix,info) error("cannot handle "..prefix) end
> >
> > while true do
> > local prefix, info = line:sub(1,3), line:sub(4)
> > local h = handlers[prefix] or badprefix
> > h(prefix,info)
> > end
> >
>
> ...whow!...
>
> But how can I handle different length of prefixes with directly
> following data... ?
local prefix = serialport:read(1)
if prefix == ONE_CHAR_PREFIX then
local data = serialport:read(based-on-prefix)
else
prefix2 = serialport:read(1)
-- now, use prefix and prefix2 to determine if you have
-- all the data, or if you need to read one more byte
end
-spc