X-Git-Url: https://oss.titaniummirror.com/gitweb?a=blobdiff_plain;f=libstdc%2B%2B-v3%2Fdoc%2Fxml%2Fmanual%2Fmessages.xml;fp=libstdc%2B%2B-v3%2Fdoc%2Fxml%2Fmanual%2Fmessages.xml;h=dcb504a35d8a5045f24121175deb987d98bc3506;hb=6fed43773c9b0ce596dca5686f37ac3fc0fa11c0;hp=0000000000000000000000000000000000000000;hpb=27b11d56b743098deb193d510b337ba22dc52e5c;p=msp430-gcc.git diff --git a/libstdc++-v3/doc/xml/manual/messages.xml b/libstdc++-v3/doc/xml/manual/messages.xml new file mode 100644 index 00000000..dcb504a3 --- /dev/null +++ b/libstdc++-v3/doc/xml/manual/messages.xml @@ -0,0 +1,604 @@ + + + + + + + ISO C++ + + + messages + + + + +messages + + +The std::messages facet implements message retrieval functionality +equivalent to Java's java.text.MessageFormat .using either GNU gettext +or IEEE 1003.1-200 functions. + + + +Requirements + + +The std::messages facet is probably the most vaguely defined facet in +the standard library. It's assumed that this facility was built into +the standard library in order to convert string literals from one +locale to the other. For instance, converting the "C" locale's +const char* c = "please" to a German-localized "bitte" +during program execution. + + +
+ +22.2.7.1 - Template class messages [lib.locale.messages] + +
+ + +This class has three public member functions, which directly +correspond to three protected virtual member functions. + + + +The public member functions are: + + + +catalog open(const string&, const locale&) const + + + +string_type get(catalog, int, int, const string_type&) const + + + +void close(catalog) const + + + +While the virtual functions are: + + + +catalog do_open(const string&, const locale&) const + +
+ + +-1- Returns: A value that may be passed to get() to retrieve a +message, from the message catalog identified by the string name +according to an implementation-defined mapping. The result can be used +until it is passed to close(). Returns a value less than 0 if no such +catalog can be opened. + + +
+ + +string_type do_get(catalog, int, int, const string_type&) const + +
+ + +-3- Requires: A catalog cat obtained from open() and not yet closed. +-4- Returns: A message identified by arguments set, msgid, and dfault, +according to an implementation-defined mapping. If no such message can +be found, returns dfault. + + +
+ + +void do_close(catalog) const + +
+ + +-5- Requires: A catalog cat obtained from open() and not yet closed. +-6- Effects: Releases unspecified resources associated with cat. +-7- Notes: The limit on such resources, if any, is implementation-defined. + + +
+ + + + + +Design + + +A couple of notes on the standard. + + + +First, why is messages_base::catalog specified as a typedef +to int? This makes sense for implementations that use +catopen, but not for others. Fortunately, it's not heavily +used and so only a minor irritant. + + + +Second, by making the member functions const, it is +impossible to save state in them. Thus, storing away information used +in the 'open' member function for use in 'get' is impossible. This is +unfortunate. + + + +The 'open' member function in particular seems to be oddly +designed. The signature seems quite peculiar. Why specify a const +string& argument, for instance, instead of just const +char*? Or, why specify a const locale& argument that is +to be used in the 'get' member function? How, exactly, is this locale +argument useful? What was the intent? It might make sense if a locale +argument was associated with a given default message string in the +'open' member function, for instance. Quite murky and unclear, on +reflection. + + + +Lastly, it seems odd that messages, which explicitly require code +conversion, don't use the codecvt facet. Because the messages facet +has only one template parameter, it is assumed that ctype, and not +codecvt, is to be used to convert between character sets. + + + +It is implicitly assumed that the locale for the default message +string in 'get' is in the "C" locale. Thus, all source code is assumed +to be written in English, so translations are always from "en_US" to +other, explicitly named locales. + + + + + +Implementation + + + Models + + This is a relatively simple class, on the face of it. The standard + specifies very little in concrete terms, so generic + implementations that are conforming yet do very little are the + norm. Adding functionality that would be useful to programmers and + comparable to Java's java.text.MessageFormat takes a bit of work, + and is highly dependent on the capabilities of the underlying + operating system. + + + + Three different mechanisms have been provided, selectable via + configure flags: + + + + + + generic + + + This model does very little, and is what is used by default. + + + + + + gnu + + + The gnu model is complete and fully tested. It's based on the + GNU gettext package, which is part of glibc. It uses the + functions textdomain, bindtextdomain, gettext to + implement full functionality. Creating message catalogs is a + relatively straight-forward process and is lightly documented + below, and fully documented in gettext's distributed + documentation. + + + + + + ieee_1003.1-200x + + + This is a complete, though untested, implementation based on + the IEEE standard. The functions catopen, catgets, + catclose are used to retrieve locale-specific messages + given the appropriate message catalogs that have been + constructed for their use. Note, the script + po2msg.sed that is part of the gettext distribution can + convert gettext catalogs into catalogs that + catopen can use. + + + + + +A new, standards-conformant non-virtual member function signature was +added for 'open' so that a directory could be specified with a given +message catalog. This simplifies calling conventions for the gnu +model. + + + + + + The GNU Model + + + The messages facet, because it is retrieving and converting + between characters sets, depends on the ctype and perhaps the + codecvt facet in a given locale. In addition, underlying "C" + library locale support is necessary for more than just the + LC_MESSAGES mask: LC_CTYPE is also + necessary. To avoid any unpleasantness, all bits of the "C" mask + (i.e. LC_ALL) are set before retrieving messages. + + + + Making the message catalogs can be initially tricky, but become + quite simple with practice. For complete info, see the gettext + documentation. Here's an idea of what is required: + + + + + + Make a source file with the required string literals that need + to be translated. See intl/string_literals.cc for + an example. + + + + + + Make initial catalog (see "4 Making the PO Template File" from + the gettext docs). + + xgettext --c++ --debug string_literals.cc -o libstdc++.pot + + + + + Make language and country-specific locale catalogs. + + cp libstdc++.pot fr_FR.po + + + cp libstdc++.pot de_DE.po + + + + + + Edit localized catalogs in emacs so that strings are + translated. + + + emacs fr_FR.po + + + + + Make the binary mo files. + + msgfmt fr_FR.po -o fr_FR.mo + + + msgfmt de_DE.po -o de_DE.mo + + + + + Copy the binary files into the correct directory structure. + + cp fr_FR.mo (dir)/fr_FR/LC_MESSAGES/libstdc++.mo + + + cp de_DE.mo (dir)/de_DE/LC_MESSAGES/libstdc++.mo + + + + + Use the new message catalogs. + + locale loc_de("de_DE"); + + + + use_facet<messages<char> >(loc_de).open("libstdc++", locale(), dir); + + + + + + + + + +Use + + A simple example using the GNU model of message conversion. + + + +#include <iostream> +#include <locale> +using namespace std; + +void test01() +{ + typedef messages<char>::catalog catalog; + const char* dir = + "/mnt/egcs/build/i686-pc-linux-gnu/libstdc++/po/share/locale"; + const locale loc_de("de_DE"); + const messages<char>& mssg_de = use_facet<messages<char> >(loc_de); + + catalog cat_de = mssg_de.open("libstdc++", loc_de, dir); + string s01 = mssg_de.get(cat_de, 0, 0, "please"); + string s02 = mssg_de.get(cat_de, 0, 0, "thank you"); + cout << "please in german:" << s01 << '\n'; + cout << "thank you in german:" << s02 << '\n'; + mssg_de.close(cat_de); +} + + + + + +Future + + + + + Things that are sketchy, or remain unimplemented: + + + + + _M_convert_from_char, _M_convert_to_char are in flux, + depending on how the library ends up doing character set + conversions. It might not be possible to do a real character + set based conversion, due to the fact that the template + parameter for messages is not enough to instantiate the + codecvt facet (1 supplied, need at least 2 but would prefer + 3). + + + + + + There are issues with gettext needing the global locale set + to extract a message. This dependence on the global locale + makes the current "gnu" model non MT-safe. Future versions + of glibc, i.e. glibc 2.3.x will fix this, and the C++ library + bits are already in place. + + + + + + + + Development versions of the GNU "C" library, glibc 2.3 will allow + a more efficient, MT implementation of std::messages, and will + allow the removal of the _M_name_messages data member. If this is + done, it will change the library ABI. The C++ parts to support + glibc 2.3 have already been coded, but are not in use: once this + version of the "C" library is released, the marked parts of the + messages implementation can be switched over to the new "C" + library functionality. + + + + + At some point in the near future, std::numpunct will probably use + std::messages facilities to implement truename/falsename + correctly. This is currently not done, but entries in + libstdc++.pot have already been made for "true" and "false" string + literals, so all that remains is the std::numpunct coding and the + configure/make hassles to make the installed library search its + own catalog. Currently the libstdc++.mo catalog is only searched + for the testsuite cases involving messages members. + + + + + The following member functions: + + + + catalog + open(const basic_string<char>& __s, const locale& __loc) const + + + + + + catalog + open(const basic_string<char>&, const locale&, const char*) const; + + + + + Don't actually return a "value less than 0 if no such catalog + can be opened" as required by the standard in the "gnu" + model. As of this writing, it is unknown how to query to see + if a specified message catalog exists using the gettext + package. + + + + + + + +Bibliography + + + + The GNU C Library + + + + McGrath + Roland + + + Drepper + Ulrich + + + + 2007 + FSF + + Chapters 6 Character Set Handling, and 7 Locales and Internationalization + + + + + + + Correspondence + + + + Drepper + Ulrich + + + + 2002 + + + + + + + ISO/IEC 14882:1998 Programming languages - C++ + + + + 1998 + ISO + + + + + + ISO/IEC 9899:1999 Programming languages - C + + + + 1999 + ISO + + + + + + System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x) + + + + 1999 + + The Open Group/The Institute of Electrical and Electronics Engineers, Inc. + + + + + + + + + + + + The C++ Programming Language, Special Edition + + + + Stroustrup + Bjarne + + + + 2000 + Addison Wesley, Inc. + + Appendix D + + + + Addison Wesley + + + + + + + + + Standard C++ IOStreams and Locales + + + Advanced Programmer's Guide and Reference + + + + Langer + Angelika + + + + Kreft + Klaus + + + + 2000 + Addison Wesley Longman, Inc. + + + + + Addison Wesley Longman + + + + + + + + Java 2 Platform, Standard Edition, v 1.3.1 API Specification + + java.util.Properties, java.text.MessageFormat, +java.util.Locale, java.util.ResourceBundle + + + + + + + + + GNU gettext tools, version 0.10.38, Native Language Support +Library and Tools. + + + + + + + + + +