   
   
   
   
   
  
  Notes on the ctype implementation.
  
prepared by Benjamin Kosnik (bkoz@redhat.com) on August 30, 2000
1. Abstract
Woe is me.
2. What the standard says
3. Problems with "C" ctype : global locales, termination.
For the required specialization codecvt<wchar_t, char, mbstate_t> ,
conversions are made between the internal character set (always UCS4
on GNU/Linux) and whatever the currently selected locale for the
LC_CTYPE category implements.
4. Design
The two required specializations are implemented as follows:
ctype<char>
This is simple specialization. Implementing this was a piece of cake.
ctype<wchar_t>
This specialization, by specifying all the template parameters, pretty
much ties the hands of implementors. As such, the implementation is
straightforward, involving mcsrtombs for the conversions between char
to wchar_t and wcsrtombs for conversions between wchar_t and char.
Neither of these two required specializations deals with Unicode
characters. As such, libstdc++-v3 implements 
5.  Examples
  typedef ctype<char> cctype;
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
   
 how to deal with the global locale issue?    
 how to deal with different types than char, wchar_t?    
 codecvt/ctype overlap: narrow/widen    
 mask typedef in codecvt_base, argument types in codecvt.
   what is know about this type? 
   
 why mask* argument in codecvt?    
   
 can this be made (more) generic? is there a simple way to
   straighten out the configure-time mess that is a by-product of
   this class? 
   
 get the ctype<wchar_t>::mask stuff under control. Need to
   make some kind of static table, and not do lookup evertime
   somebody hits the do_is... functions. Too bad we can't just
   redefine mask for ctype<wchar_t> 
   
   
 rename abstract base class. See if just smash-overriding
   is a better approach. Clarify, add sanity to naming. 
7. Acknowledgments
Ulrich Drepper for patient answering of late-night questions, skeletal
examples, and C language expertise.
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
