文件名称：LuaUnicode icu-lua
文件大小：154KB
文件格式：RAR
更新时间：2013-09-12 17:43:36
lua luaUincode
来源： http://lua-users.org/wiki/LuaUnicode 目录： | LuaUnicode.url | +---0.13A | ICU4Lua-0.13A-src.zip | ICU4Lua-0.13A-win32-dll.zip | \---0.2B ICU4Lua-0.2B-docs.zip ICU4Lua-0.2B-src.zip ICU4Lua-0.2B-win32dll.zip 下面的来源于： http://lua-users.org/wiki/LuaUnicode This is an attempt to answer the LuaFaq : Can I use unicode strings? or Does Lua support unicode? In short, yes and no. Lua gives you the bare bones support and enough rope and not much else. Unicode is a large and complex standard and questions like "does lua support unicode" are extremely vague. Some of the issues are: Can I store and retrieve Unicode strings? Can my Lua programs be written in Unicode? Can I compare Unicode strings for equality? Sorting strings. Pattern matching. Can I determine the length of a Unicode string? Support for bracket matching, bidirectional printing, arbitrary composition of characters, and other issues that arise in high quality typesetting. Lua strings are fully 8-bit clean, so simple uses are supported (like storing and retrieving), but there's no built in support for more sophisticated uses. For a fuller story, see below. Unicode strings and Lua strings A Lua string is an aribitrary sequence of values which have at least 8 bits (octets); they map directly into the char type of the C compiler. (This may be wider than eight bits, but eight bits are guaranteed.) Lua does not reserve any value, including NUL. That means that you can store a UTF-8 string in Lua without problems. Note that UTF-8 is just one option for storing Unicode strings. There are many other encoding schemes, including UTF-16 and UTF-32 and their various big-endian/little-endian variants. However, all of these are simply sequences of octets and can be stored in a Lua string without problems. Input and output of strings in Lua (using the io library) uses C's stdio library. ANSI C does not require the stdio library to handle arbitrary octet sequences unless the file is opened in binary mode; furthermore, in non-binary mode, some octet sequences are converted into other ones (in order to deal with varying end-of-line markers on different platforms). This may affect your ability to do non-binary file input and output of Unicode strings in formats other than UTF-8. UTF-8 strings will probably be safe because UTF-8 does not use control characters such as \n and \r as part of multi-octet encodings. However, there are no guarantees; if you need to be certain, you must use binary mode input and output. (If you do so, line-endings will not be converted.) Unix file IO has been 8-bit clean for a long while. If you are not concerned with portability and are only using Unix and Unix-like operating systems, you can almost certainly not worry about the above. If your use of Unicode is restricted to passing the strings to external libraries which support Unicode, you should be OK. For example, you should be able to extract a Unicode string from a database and pass it to a Unicode-aware graphics library. But see the sections below on pattern matching and string equality. Unicode Lua programs Literal Unicode strings can appear in your lua programs. Either a UTF-8 encoded string can appear directly with 8-bit characters or you can use the \ddd syntax (note that ddd is a decimal number, unlike some other languages). However, there is no facility for encoding multi-octet sequences (such as \U+20B4); you would need to either manually encode them to UTF-8, or insert individual octets in the correct big-endian/little-endian order (for UTF-16 or UTF-32). Unless you are using an operating system in which a char is more than eight bits wide, you will not be able to use arbitrary Unicode characters in Lua identifers (for the names of variables and so on). You may be able to use eight-bit characters outside of the ANSI range. Lua uses the C functions isalpha and isalnum to identify valid characters in identifiers, so it will depend on the current locale. To be honest, using characters outside of the ANSI range in Lua identifiers is not a good idea, since your programs will not compile in the standard C locale. Comparison and Sorting Lua string comparison (using the == operator) is done byte-by-byte. That means that == can only be used to compare Unicode strings for equality if the strings have been normalized in one of the four Unicode normalizations. (See the [Unicode FAQ on normalization] for details.) The standard Lua library does not provide any facility for normalizing Unicode strings. Consequently, non-normalized Unicode strings cannot be reliably used as table keys. If you want to use the Unicode notion of string equality, or use Unicode strings as table keys, and you cannot guarantee that your strings are normalized, then you'll have to write or find a normalization function and use that; this is non-trivial exercise! The Lua comparison operators on strings (< and <=) use the C function strcoll which is locale dependent. This means that two strings can compare in different ways according to what the current locale is. For example, strings will compare differently when using Spanish Traditional sorting to that when using Welsh sorting. It may be that your operating system has a locale that implements the sorting algorithm that you want, in which case you can just use that, otherwise you will have to write a function to sort Unicode strings. This is an even more non-trivial exercise. UTF-8 was designed so that a naive octet-by-octet string comparison of an octet sequence would produce the same result if a naive octet-by-octet string comparison were done on the UTF-8 encoding of the octet sequence. This is also true of UTF-32BE but I do not know of any system which uses that encoding. Unfortunately, naive octet-by-octet comparison is not the collation order used by any language. (Note: sometimes people use the terms UCS-2 and UCS-4 for "two-byte" and four-byte encodings. These are not Unicode standards; they come from the closely corresponding ISO standard ISO/IEC 10646-1:2000 and currently differ in that they allow codes outside of the Unicode range, which runs from 0x0 to 0x10FFFF.) Pattern Matching Lua's pattern matching facilities work character by character. In general, this will not work for Unicode pattern matching, although some things will work as you want. For example, "%u" will not match all Unicode upper case letters. You can match individual Unicode characters in a normalized Unicode string, but you might want to worry about combining character sequences. If there are no following combining characters, "a" will match only the letter a in a UTF-8 string. In UTF-16LE you could match "a%z". (Remember that you cannot use \0 in a Lua pattern.) Length and string indexing If you want to know the length of a Unicode string there are different answers you might want according to the circumstances. If you just want to know how many bytes the string occupies, so that you can make space for copying it into a buffer for example, then the existing Lua function string.len will work. You might want to know how many Unicode characters are in a string. Depending on the encoding used, a single Unicode character may occupy up to four bytes. Only UTF-32LE and UTF-32BE are constant length encodings (four bytes per character); UTF-32 is mostly a constant length encoding but the first element in a UTF-32 sequence should be a "Byte Order Mark", which does not count as a character. (UTF-32 and variants are part of Unicode with the latest version, Unicode 4.0.) Some implementations of UTF-16 assume that all characters are two bytes long, but this has not been true since Unicode version 3.0. Happily UTF-8 is designed so that it is relatively easy to count the number of unicode symbols in a string: simply count the number of octets that are in the ranges 0x00 to 0x7f (inclusive) or 0xC2 to 0xF4 (inclusive). (In decimal, 0-127 and 194-244.) These are the codes which can start a UTF-8 character code. Octets 0xC0, 0xC1 and 0xF5 to 0xFF (192, 193 and 245-255) cannot appear in a conforming UTF-8 sequence; octets in the range 0x80 to 0xBF (128-191) can only appear in the second and subsequent octets of a multi-octet encoding. Remember that you cannot use \0 in a Lua pattern. For example, you could use the following code snippet to count UTF-8 characters in a string you knew to be conforming (it will incorrectly count some invalid characters): local _, count = string.gsub(unicode_string, "[^\128-\193]", "") If you want to know how many printing columns a Unicode string will occupy when you print it out using a fixed-width font (imagine you are writing something like the Unix ls program that formats its output into several columns), then that is a different answer again. That's because some Unicode characters do not have a printing width, while others are double-width characters. Combining characters are used to add accents to other letters, and generally they do not take up any extra space when printed. So that's at least 3 different notions of length that you might want at different times. Lua provides one of them (string.len) the others you'll need to write functions for. There's a similar issue with indexing the characters of a string by position. string.sub(s, -3) will return the last 3 bytes of the string which is not necessarily the same as the last three characters of the string, and may or may not be a complete code. You could use the following code snippet to iterate over UTF-8 sequences (this will simply skip over most invalid codes): for uchar in string.gfind(ustring, "([%z\1-\127\194-\244][\128-\191]*)") do -- something end More sophisticated issues As you might have guessed by now, Lua provides no support for things like bidirectional printing or the proper formatting of Thai accents. Normally such things will be taken care of by a graphics or typography library. It would of course be possible to interface to such a library that did these things if you had access to one. There is a little string-like package [slnunicode] with upper/lower, len/sub and pattern matching for UTF-8. See ValidateUnicodeString for a smaller library. [ICU4Lua] is a Lua binding to ICU (International Components for Unicode [1]), an open-source library originally developed by IBM. See UnicodeIdentifers for platform independent Unicode Lua programs.
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