How to convert UTF8 byte arrays to string in lua - utf-8

Question

I have a table like this
table = {57,55,0,15,-25,139,130,-23,173,148,-24,136,158}
it is utf8 encoded byte array by php unpack function
unpack('C*',$str);
how can I convert it to utf-8 string I can read in lua?

Answer 1

Lua doesn't provide a direct function for turning a table of utf-8 bytes in numeric form into a utf-8 string literal. But it's easy enough to write something for this with the help of string.char:
function utf8_from(t)
local bytearr = {}
for _, v in ipairs(t) do
local utf8byte = v < 0 and (0xff + v + 1) or v
table.insert(bytearr, string.char(utf8byte))
end
return table.concat(bytearr)
end
Note that none of lua's standard functions or provided string facilities are utf-8 aware. If you try to print utf-8 encoded string returned from the above function you'll just see some funky symbols. If you need more extensive utf-8 support you'll want to check out some of the libraries mention from the lua wiki.

Answer 2

Here's a comprehensive solution that works for the UTF-8 character set restricted by RFC 3629:
do
local bytemarkers = { {0x7FF,192}, {0xFFFF,224}, {0x1FFFFF,240} }
function utf8(decimal)
if decimal<128 then return string.char(decimal) end
local charbytes = {}
for bytes,vals in ipairs(bytemarkers) do
if decimal<=vals[1] then
for b=bytes+1,2,-1 do
local mod = decimal%64
decimal = (decimal-mod)/64
charbytes[b] = string.char(128+mod)
end
charbytes[1] = string.char(vals[2]+decimal)
break
end
end
return table.concat(charbytes)
end
end
function utf8frompoints(...)
local chars,arg={},{...}
for i,n in ipairs(arg) do chars[i]=utf8(arg[i]) end
return table.concat(chars)
end
print(utf8frompoints(72, 233, 108, 108, 246, 32, 8364, 8212))
--> Héllö €—