用 Lua 提取 UTF-8 字符串的第一个字母 [英] Extract the first letter of a UTF-8 string with Lua

问题描述

有没有办法用Lua提取UTF-8编码字符串的第一个字母?

Is there any way to extract the first letter of a UTF-8 encoded string with Lua?

Lua 没有正确支持 Unicode，所以 string.sub("ÆØÅ", 2, 2) 将返回 "?" 而不是 "Ø".

Lua does not properly support Unicode, so string.sub("ÆØÅ", 2, 2) will return "?" rather than "Ø".

是否有一个相对简单的 UTF-8 解析算法，我可以在每个字节的字符串字节上使用，其唯一目的是获取字符串的第一个字母，是汉字还是 A?

Is there a relatively simple UTF-8 parsing algorithm I could use on the string byte per byte, for the sole purpose of getting the first letter of the string, be it a Chinese character or an A?

还是这种方式太复杂，需要庞大的库等?

Or is this way too complex, requiring a huge library, etc.?

推荐答案

您可以使用以下代码轻松地从 UTF-8 编码的字符串中提取第一个字母:

You can easily extract the first letter from a UTF-8 encoded string with the following code:

function firstLetter(str)
  return str:match("[%z1-127194-244][128-191]*")
end

因为 UTF-8 代码点要么以 0 到 127 的字节开头，要么以 194 到 244 的字节后跟一个或多个 128 到 191 的字节开始.

Because a UTF-8 code point either begins with a byte from 0 to 127, or with a byte from 194 to 244 followed by one or several bytes from 128 to 191.

您甚至可以以类似的方式迭代 UTF-8 代码点:

You can even iterate over UTF-8 code points in a similar manner:

for code in str:gmatch("[%z1-127194-244][128-191]*") do
  print(code)
end

请注意，两个示例都为每个字母返回一个 string 值，而不是 Unicode 代码点数值.

Note that both examples return a string value for each letter, and not the Unicode code point numerical value.

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