Notes on the locale implementation.
prepared by Benjamin Kosnik (bkoz@redhat.com) on January 24, 2001
1. Abstract Describes the basic locale object, including nested
classes id, facet, and the reference-counted implementation object,
class _Impl.
2. What the standard says
See Chapter 22 of the standard.
3. Problems with "C" locales : global locales, termination.
The major problem is fitting an object-orientated and non-global locale
design ontop of POSIX and other relevant stanards, which include the
Single Unix (nee X/Open.)
Because POSIX falls down so completely, portibility is an issue.
4. Design
Class locale in non-templatized and has three distinct types nested
inside of it:
class facet
22.1.1.1.2 Class locale::facet
Facets actually implement locale functionality. For instance, a facet
called numpunct is the data objects that can be used to query for the
thousands seperator is in the German locale.
Literally, a facet is strictly defined:
- containing
public:
static locale::id id;
- or derived from another facet
The only other thing of interest in this class is the memory
management of facets. Each constructor of a facet class takes a
std::size_t __refs argument: if __refs == 0, the facet is deleted when
no longer used. if __refs == 1, the facet is not destroyed, even when
it is no longer reference.
class id
Provides an index for looking up specific facets.
class _Impl
5. Examples
typedef __locale_t locale;
More information can be found in the following testcases:
- testsuite/22_locale/ctype_char_members.cc
- testsuite/22_locale/ctype_wchar_t_members.cc
6. Unresolved Issues
- locale -a displays available locales on linux
- locale initialization: at what point does _S_classic,
_S_global get initialized? Can named locales assume this
initialization has already taken place?
7. Acknowledgments
8. Bibliography / Referenced Documents
Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters "6. Character Set Handling" and "7 Locales and Internationalization"
Drepper, Ulrich, Numerous, late-night email correspondence
ISO/IEC 14882:1998 Programming languages - C++
ISO/IEC 9899:1999 Programming languages - C
Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000
Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000
System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x)
The Open Group/The Institute of Electrical and Electronics Engineers, Inc.
http://www.opennc.org/austin/docreg.html