C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Universal character name question          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message Alberto Ganesh Barbati Guest Posted: Tue Oct 03, 2006 10:09 pm    Post subject: Universal character name question Hi Everybody, in §2.3/2 it is said: "if the universal character name designates a character in the basic source character set, then the program is ill-formed." I wonder what is the rationale for this restriction. I mean, what's wrong in writing "\u0055niversal" instead of "Universal" (except obfuscation, of course)? Doesn't this restriction make the use of universal character names inherently non-portable? As I am not aware of the basic source character set of every possible platform, whenever I use a universal character I run the risk of designating some forbidden character on some platform and so my code would be ill-formed there. In Annex E there's a list of universal characters names allowed in identifiers. According to §2.3/2 I can have an identifier named \u00c0 but not \u0041, although the character U+0041 is listed as valid in the annex. It seems a strange and gratuitous asymmetry to me. Not that I'm going to use universal characters all over the place... It's just a curiosity. Ganesh --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Guest Posted: Wed Oct 04, 2006 4:45 am    Post subject: Re: Universal character name question Alberto Ganesh Barbati wrote: Quote: Hi Everybody, in §2.3/2 it is said: "if the universal character name designates a character in the basic source character set, then the program is ill-formed." I wonder what is the rationale for this restriction. I mean, what's wrong in writing "\u0055niversal" instead of "Universal" (except obfuscation, of course)? Doesn't this restriction make the use of universal character names inherently non-portable? As I am not aware of the basic source character set of every possible platform, You should be. It's a list of exactly 96 characters, which is by definition exactly the same on every conforming implementation of C++. See 2.2p1 for the list. As a result, there's no danger of the following: Quote: ... whenever I use a universal character I run the risk of designating some forbidden character on some platform and so my code would be ill-formed there. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Greg Herlihy Guest Posted: Wed Oct 04, 2006 4:09 pm    Post subject: Re: Universal character name question Alberto Ganesh Barbati wrote: Quote: Hi Everybody, in §2.3/2 it is said: "if the universal character name designates a character in the basic source character set, then the program is ill-formed." I wonder what is the rationale for this restriction. I mean, what's wrong in writing "\u0055niversal" instead of "Universal" (except obfuscation, of course)? Probably to keep identifier names canonical. After all, 512 different ways to write the "universal" as an identifiier seems a needless complication. Quote: Doesn't this restriction make the use of universal character names inherently non-portable? As I am not aware of the basic source character set of every possible platform, whenever I use a universal character I run the risk of designating some forbidden character on some platform and so my code would be ill-formed there. No, there is no portability issue because the source character set (and the set of allowed universal names in identifiers) is the same across all implementations. So you'll never have a problem porting a source file due to its use of universal character names. The question is moot anyway because the contents of a C++ source file is completely non-portable to start with. The mapping of a source file's contents to the source character set is "implementation-defined." So the Standard doesn't offer much assistance to get a set of ASCII source files to compile with an implementation that expects characters in EBCDIC. Quote: In Annex E there's a list of universal characters names allowed in identifiers. According to §2.3/2 I can have an identifier named \u00c0 but not \u0041, although the character U+0041 is listed as valid in the annex. It seems a strange and gratuitous asymmetry to me. Annex E explicity excludes the ranges u+0041 - u+0051 and u+0061 - u+007a from the set of universal names that may be used in an identifier. Greg --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top kanze Guest Posted: Wed Oct 04, 2006 5:21 pm    Post subject: Re: Universal character name question Alberto Ganesh Barbati wrote: Quote: in §2.3/2 it is said: "if the universal character name designates a character in the basic source character set, then the program is ill-formed." I wonder what is the rationale for this restriction. I mean, what's wrong in writing "\u0055niversal" instead of "Universal" (except obfuscation, of course)? I think that the intent is to allow several different interal encodings. In particular, to allow the implementation to either keep the extended characters in the \u0055 format (in the string), or to translate it into whatever character corresponds in the native environment. In the first case, the string "\u0055" doesn't compare equal to "U". For typical systems, which actually support an extended native character set, this freedom doesn't buy much, since they already have to handle the case that "é" and "\u00e5" must compare equal. The obvious solution is to maintain symbol names as 32 bit integers, with the universal character names replaced internally by a single Unicode character. But the standard doesn't mandate this, and on an implementation with very limited resources, it would be quite reasonable (and legal) to only accept universal character names for extended characters, and store the symbol names exactly as they were read. Allowing code to use "\u0055niversal" instead of "Universal" would require special handling in such implementations. Quote: Doesn't this restriction make the use of universal character names inherently non-portable? In some contexts, they are. If you write std::cout << "\u00E5t\u00E5\n" ; and output it to a device which only supports the 128 basic ASCII characters, you're going to loose something. Quote: As I am not aware of the basic source character set of every possible platform, It's defined in the standard. See §2.2. Quote: whenever I use a universal character I run the risk of designating some forbidden character on some platform and so my code would be ill-formed there. Less so than if you write a file using CRLF as line separators, on Windows, and try to compile it with some implementations under Unix. Quote: In Annex E there's a list of universal characters names allowed in identifiers. According to §2.3/2 I can have an identifier named \u00c0 but not \u0041, although the character U+0041 is listed as valid in the annex. It seems a strange and gratuitous asymmetry to me. U+0041 is not listed as a valid univeral character name in Appendix E of the current draft. Any of the 96 characters in the basic source character set defined in §2.2 must appear literally. In portable code, any other character (including @ or $) must appear as a universal character name. Implementations are allowed (and even encouranged, if I'm reading between the lines in §2.1/1 correctly) to support any other characters in the native character set, but they must do so in a manner which makes them indistinguishable from their universal character name equivalent. And if you copy the file to a system where the character in question isn't in the native character set, then there's no guarantee that your code will compile. The ideal solution, of course, is that the set of tools associated with the compiler (e.g. editor, etc.) permit entry of and display the characters as best it can, given the resources available to it, but that it actually store them in the files as universal character names. But I don't know of any system which does this, and it sort of goes against the basic philosophy of Unix, in which text is text, and any program which handles text can handle just about any text file. -- James Kanze GABI Software Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Alberto Ganesh Barbati Guest Posted: Wed Oct 04, 2006 9:22 pm    Post subject: Re: Universal character name question kuyper (AT) wizard (DOT) net ha scritto: Quote: Alberto Ganesh Barbati wrote: Hi Everybody, in §2.3/2 it is said: "if the universal character name designates a character in the basic source character set, then the program is ill-formed." I wonder what is the rationale for this restriction. I mean, what's wrong in writing "\u0055niversal" instead of "Universal" (except obfuscation, of course)? Doesn't this restriction make the use of universal character names inherently non-portable? As I am not aware of the basic source character set of every possible platform, You should be. It's a list of exactly 96 characters, which is by definition exactly the same on every conforming implementation of C++. See 2.2p1 for the list. As a result, there's no danger of the following: Ah, yes, sure. I had read 2.2p1 but I missed footnote 15 and probably also got confused by the many character sets... Thanks. However, this doesn't answer my original question: why is the restriction there in the first place? Why can't I write \u0041 in my source code? Ganesh --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Guest Posted: Mon Oct 09, 2006 3:55 pm    Post subject: Re: Universal character name question Alberto Ganesh Barbati wrote: Quote: "if the universal character name designates a character in the basic source character set, then the program is ill-formed." I wonder what is the rationale for this restriction. I mean, what's wrong in writing "\u0055niversal" instead of "Universal" (except obfuscation, of course)? What about "\\u00750055niversal" ? "\u005c0055niversal"? Under the current rules we don't have to consider escaped escape characters. HTH, Michiel Salters --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top Alberto Ganesh Barbati Guest Posted: Mon Oct 09, 2006 11:01 pm    Post subject: Re: Universal character name question Michiel.Salters (AT) tomtom (DOT) com ha scritto: Quote: What about "\\u00750055niversal" ? "\u005c0055niversal"? Under the current rules we don't have to consider escaped escape characters. The second string is surely ill-formed because \u005c is in the basic source character set. About the first one, I'm not sure... if I read the standard correctly, conversion to the execution character set of escape sequences and universal-character-names in string literals happens simultaneously in translation phase 5. So the resulting literal should be a backslash + "00750055niversal". Ganesh --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ] Back to top kanze Guest Posted: Tue Oct 10, 2006 3:31 pm    Post subject: Re: Universal character name question Alberto Ganesh Barbati wrote: Quote: Michiel.Salters (AT) tomtom (DOT) com ha scritto: What about "\\u00750055niversal" ? "\u005c0055niversal"? Under the current rules we don't have to consider escaped escape characters. The second string is surely ill-formed because \u005c is in the basic source character set. But he gave the example as to why this should be the case. "\u005c" is a backslash. If you allowed universal character names for characters in the basic character set, you'd have to consider this string as equal to "Universal". Quote: About the first one, I'm not sure... if I read the standard correctly, conversion to the execution character set of escape sequences and universal-character-names in string literals happens simultaneously in translation phase 5. So the resulting literal should be a backslash + "00750055niversal". I think you're right there. -- James Kanze GABI Software Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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