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diff --git a/libstdc++-v3/doc/xml/manual/messages.xml b/libstdc++-v3/doc/xml/manual/messages.xml new file mode 100644 index 000000000..753b965e6 --- /dev/null +++ b/libstdc++-v3/doc/xml/manual/messages.xml @@ -0,0 +1,566 @@ +<section xmlns="http://docbook.org/ns/docbook" version="5.0" + xml:id="manual.localization.facet.messages" xreflabel="Messages"> +<?dbhtml filename="messages.html"?> + +<info><title>messages</title> + <keywordset> + <keyword> + ISO C++ + </keyword> + <keyword> + messages + </keyword> + </keywordset> +</info> + + + +<para> +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. +</para> + +<section xml:id="facet.messages.req"><info><title>Requirements</title></info> + + +<para> +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 +<code>const char* c = "please"</code> to a German-localized <code>"bitte"</code> +during program execution. +</para> + +<blockquote> +<para> +22.2.7.1 - Template class messages [lib.locale.messages] +</para> +</blockquote> + +<para> +This class has three public member functions, which directly +correspond to three protected virtual member functions. +</para> + +<para> +The public member functions are: +</para> + +<para> +<code>catalog open(const string&, const locale&) const</code> +</para> + +<para> +<code>string_type get(catalog, int, int, const string_type&) const</code> +</para> + +<para> +<code>void close(catalog) const</code> +</para> + +<para> +While the virtual functions are: +</para> + +<para> +<code>catalog do_open(const string&, const locale&) const</code> +</para> +<blockquote> +<para> +<emphasis> +-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. +</emphasis> +</para> +</blockquote> + +<para> +<code>string_type do_get(catalog, int, int, const string_type&) const</code> +</para> +<blockquote> +<para> +<emphasis> +-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. +</emphasis> +</para> +</blockquote> + +<para> +<code>void do_close(catalog) const</code> +</para> +<blockquote> +<para> +<emphasis> +-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. +</emphasis> +</para> +</blockquote> + + +</section> + +<section xml:id="facet.messages.design"><info><title>Design</title></info> + + +<para> +A couple of notes on the standard. +</para> + +<para> +First, why is <code>messages_base::catalog</code> specified as a typedef +to int? This makes sense for implementations that use +<code>catopen</code>, but not for others. Fortunately, it's not heavily +used and so only a minor irritant. +</para> + +<para> +Second, by making the member functions <code>const</code>, 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. +</para> + +<para> +The 'open' member function in particular seems to be oddly +designed. The signature seems quite peculiar. Why specify a <code>const +string& </code> argument, for instance, instead of just <code>const +char*</code>? Or, why specify a <code>const locale&</code> 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. +</para> + +<para> +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. +</para> + +<para> +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. +</para> + +</section> + +<section xml:id="facet.messages.impl"><info><title>Implementation</title></info> + + + <section xml:id="messages.impl.models"><info><title>Models</title></info> + + <para> + 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. + </para> + + <para> + Three different mechanisms have been provided, selectable via + configure flags: + </para> + +<itemizedlist> + <listitem> + <para> + generic + </para> + <para> + This model does very little, and is what is used by default. + </para> + </listitem> + + <listitem> + <para> + gnu + </para> + <para> + 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 <code>textdomain, bindtextdomain, gettext</code> 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. + </para> + </listitem> + + <listitem> + <para> + ieee_1003.1-200x + </para> + <para> + This is a complete, though untested, implementation based on + the IEEE standard. The functions <code>catopen, catgets, + catclose</code> are used to retrieve locale-specific messages + given the appropriate message catalogs that have been + constructed for their use. Note, the script <code> + po2msg.sed</code> that is part of the gettext distribution can + convert gettext catalogs into catalogs that + <code>catopen</code> can use. + </para> + </listitem> +</itemizedlist> + +<para> +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. +</para> + + </section> + + <section xml:id="messages.impl.gnu"><info><title>The GNU Model</title></info> + + + <para> + 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 + <code>LC_MESSAGES</code> mask: <code>LC_CTYPE</code> is also + necessary. To avoid any unpleasantness, all bits of the "C" mask + (i.e. <code>LC_ALL</code>) are set before retrieving messages. + </para> + + <para> + 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: + </para> + +<itemizedlist> + <listitem> + <para> + Make a source file with the required string literals that need + to be translated. See <code>intl/string_literals.cc</code> for + an example. + </para> + </listitem> + + <listitem> + <para> + Make initial catalog (see "4 Making the PO Template File" from + the gettext docs).</para> + <para> + <code> xgettext --c++ --debug string_literals.cc -o libstdc++.pot </code> + </para> + </listitem> + + <listitem> + <para>Make language and country-specific locale catalogs.</para> + <para> + <code>cp libstdc++.pot fr_FR.po</code> + </para> + <para> + <code>cp libstdc++.pot de_DE.po</code> + </para> + </listitem> + + <listitem> + <para> + Edit localized catalogs in emacs so that strings are + translated. + </para> + <para> + <code>emacs fr_FR.po</code> + </para> + </listitem> + + <listitem> + <para>Make the binary mo files.</para> + <para> + <code>msgfmt fr_FR.po -o fr_FR.mo</code> + </para> + <para> + <code>msgfmt de_DE.po -o de_DE.mo</code> + </para> + </listitem> + + <listitem> + <para>Copy the binary files into the correct directory structure.</para> + <para> + <code>cp fr_FR.mo (dir)/fr_FR/LC_MESSAGES/libstdc++.mo</code> + </para> + <para> + <code>cp de_DE.mo (dir)/de_DE/LC_MESSAGES/libstdc++.mo</code> + </para> + </listitem> + + <listitem> + <para>Use the new message catalogs.</para> + <para> + <code>locale loc_de("de_DE");</code> + </para> + <para> + <code> + use_facet<messages<char> >(loc_de).open("libstdc++", locale(), dir); + </code> + </para> + </listitem> +</itemizedlist> + + </section> +</section> + +<section xml:id="facet.messages.use"><info><title>Use</title></info> + + <para> + A simple example using the GNU model of message conversion. + </para> + +<programlisting> +#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); +} +</programlisting> + +</section> + +<section xml:id="facet.messages.future"><info><title>Future</title></info> + + +<itemizedlist> +<listitem> + <para> + Things that are sketchy, or remain unimplemented: + </para> + <itemizedlist> + <listitem> + <para> + _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). + </para> + </listitem> + + <listitem> + <para> + 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. + </para> + </listitem> + </itemizedlist> +</listitem> + +<listitem> + <para> + 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. + </para> +</listitem> +<listitem> + <para> + 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. + </para> +</listitem> + +<listitem> + <para> The following member functions:</para> + + <para> + <code> + catalog + open(const basic_string<char>& __s, const locale& __loc) const + </code> + </para> + + <para> + <code> + catalog + open(const basic_string<char>&, const locale&, const char*) const; + </code> + </para> + + <para> + 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. + </para> +</listitem> +</itemizedlist> + +</section> + +<bibliography xml:id="facet.messages.biblio"><info><title>Bibliography</title></info> + + + <biblioentry> + <citetitle> + The GNU C Library + </citetitle> + <author><personname><surname>McGrath</surname><firstname>Roland</firstname></personname></author> + <author><personname><surname>Drepper</surname><firstname>Ulrich</firstname></personname></author> + <copyright> + <year>2007</year> + <holder>FSF</holder> + </copyright> + <pagenums>Chapters 6 Character Set Handling, and 7 Locales and Internationalization + </pagenums> + </biblioentry> + + <biblioentry> + <citetitle> + Correspondence + </citetitle> + <author><personname><surname>Drepper</surname><firstname>Ulrich</firstname></personname></author> + <copyright> + <year>2002</year> + <holder/> + </copyright> + </biblioentry> + + <biblioentry> + <citetitle> + ISO/IEC 14882:1998 Programming languages - C++ + </citetitle> + <copyright> + <year>1998</year> + <holder>ISO</holder> + </copyright> + </biblioentry> + + <biblioentry> + <citetitle> + ISO/IEC 9899:1999 Programming languages - C + </citetitle> + + <copyright> + <year>1999</year> + <holder>ISO</holder> + </copyright> + </biblioentry> + + <biblioentry> + <biblioid xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.opengroup.org/austin/" class="uri"> + </biblioid> + <citetitle> + System Interface Definitions, Issue 7 (IEEE Std. 1003.1-2008) + </citetitle> + <copyright> + <year>2008</year> + <holder> + The Open Group/The Institute of Electrical and Electronics + Engineers, Inc. + </holder> + </copyright> + </biblioentry> + + <biblioentry> + <citetitle> + The C++ Programming Language, Special Edition + </citetitle> + <author><personname><surname>Stroustrup</surname><firstname>Bjarne</firstname></personname></author> + <copyright> + <year>2000</year> + <holder>Addison Wesley, Inc.</holder> + </copyright> + <pagenums>Appendix D</pagenums> + <publisher> + <publishername> + Addison Wesley + </publishername> + </publisher> + </biblioentry> + + <biblioentry> + <citetitle> + Standard C++ IOStreams and Locales + </citetitle> + <subtitle> + Advanced Programmer's Guide and Reference + </subtitle> + <author><personname><surname>Langer</surname><firstname>Angelika</firstname></personname></author> + <author><personname><surname>Kreft</surname><firstname>Klaus</firstname></personname></author> + <copyright> + <year>2000</year> + <holder>Addison Wesley Longman, Inc.</holder> + </copyright> + <publisher> + <publishername> + Addison Wesley Longman + </publishername> + </publisher> + </biblioentry> + + <biblioentry> + <biblioid xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://java.sun.com/reference/api/index.html" class="uri"> + </biblioid> + <citetitle> + API Specifications, Java Platform + </citetitle> + + <pagenums>java.util.Properties, java.text.MessageFormat, +java.util.Locale, java.util.ResourceBundle + </pagenums> + </biblioentry> + + <biblioentry> + <biblioid xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.gnu.org/software/gettext/" class="uri"> + </biblioid> + <citetitle> + GNU gettext tools, version 0.10.38, Native Language Support + Library and Tools. + </citetitle> + </biblioentry> + +</bibliography> + +</section> |