UTF-8字符串在lua中的字长问题

来源：互联网发布：bi开发工程师转行java 编辑：程序博客网时间：2024/06/05 23:53

UTF-8字符串在lua中每个字符的字长是不一样，中文，英文，其他字符。都有各自不同的字长，所以UTF-8也叫作变长字符。规则如下：

1. utf8字符是变长字符

2. 字符长度有规律

UTF-8字符规律

字符串的首个byte表示了该utf8字符的长度

0xxxxxxx - 1 byte

110yxxxx - 192, 2 byte

1110yyyy - 225, 3 byte

11110zzz - 240, 4 byte

所以，要想满足自己对字符串按字符数量截取的话，就要进行一下包装了，直接贴代码，如下：

local UTF8 = {}function UTF8.chSize(char)    if not char then        return 0    elseif char > 240 then        return 4    elseif char > 225 then        return 3    elseif char > 192 then        return 2    else        return 1    endendfunction UTF8.sub(str, startChar, numChars)    if str == nil then        return ""    end  local startIndex = 1    if (startChar==nil) then      startChar = 1;    end    if (numChars==nil) then      numChars =15;    end;    local allChars = numChars  while startChar > 1 do      local char = string.byte(str, startIndex)      startIndex = startIndex + UTF8.chSize(char)      startChar = startChar - 1  end   local currentIndex = startIndex    while currentIndex <= numChars and currentIndex <= #str do    local char = string.byte(str, currentIndex)    currentIndex = currentIndex + UTF8.chSize(char)  end    if numChars < #str then        return str:sub(startIndex, currentIndex - 1).."..."    else        return str:sub(startIndex, currentIndex - 1)    end  endfunction UTF8.length(str)local length = 0;local currentIndex = 1;while currentIndex <= #str do    local char = string.byte(str, currentIndex)    currentIndex = currentIndex + UTF8.chSize(char)    length = length + 1  end  return length;endfunction UTF8.toString(str)    if type(str)=="string" then        return str    end    local char = ""    if type(str)~="table" then        return char    end    for key, var in pairs(str) do        if var == "\0" then            break        end        char = char .. var    end    return charendreturn UTF8;

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