lua 从字符串获取指定第几位数到第几位数

– 判断utf8字符byte长度
– 0xxxxxxx - 1 byte
– 110yxxxx - 192, 2 byte
– 1110yyyy - 225, 3 byte
– 11110zzz - 240, 4 byte
local function chsize(char)
if not char then
print(“not char”)
return 0
elseif char > 240 then
return 4
elseif char > 225 then
return 3
elseif char > 192 then
return 2
else
return 1
end
end

-- 计算utf8字符串字符数, 各种字符都按一个字符计算
-- 例如utf8len("1你好") => 3
function utf8len(str)
    local len = 0
    local currentIndex = 1
    while currentIndex <= #str do
	    local char = string.byte(str, currentIndex)
	    currentIndex = currentIndex + chsize(char)
	    len = len +1
    end
    return len
end
– 截取utf8 字符串

– str: 要截取的字符串

– startChar:   开始字符下标,从1开始

– numChars:要截取的字符长度

function utf8sub(str, startChar, numChars)

local startIndex = 1

while startChar > 1 do

local char = string.byte(str, startIndex)

startIndex = startIndex + chsize(char)

startChar = startChar - 1

end
local currentIndex = startIndex

while numChars &gt; 0 and currentIndex &lt;= #str do
    local char = string.byte(str, currentIndex)
    currentIndex = currentIndex + chsize(char)
    numChars = numChars -1
end
return str:sub(startIndex, currentIndex - 1)

end
– 自测

function test()

– test utf8len

assert(utf8len("你好1世界哈哈") == 7)

assert(utf8len("你好世界1哈哈 ") == 8)

assert(utf8len(" 你好世 界1哈哈") == 9)

assert(utf8len("12345678") == 8)

assert(utf8len("øpø你好pix") == 8)
-- test utf8sub
assert(utf8sub(&#34;你好1世界哈哈&#34;,2,5) == &#34;好1世界哈&#34;)
assert(utf8sub(&#34;1你好1世界哈哈&#34;,2,5) == &#34;你好1世界&#34;)
assert(utf8sub(&#34; 你好1世界 哈哈&#34;,2,6) == &#34;你好1世界 &#34;)
assert(utf8sub(&#34;你好世界1哈哈&#34;,1,5) == &#34;你好世界1&#34;)
assert(utf8sub(&#34;12345678&#34;,3,5) == &#34;34567&#34;)
assert(utf8sub(&#34;øpø你好pix&#34;,2,5) == &#34;pø你好p&#34;)

print(&#34;all test succ&#34;)

end
test()

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