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| <h1> |
| Notes on the ctype implementation. |
| </h1> |
| <em> |
| prepared by Benjamin Kosnik (bkoz@redhat.com) on August 30, 2000 |
| </em> |
| |
| <h2> |
| 1. Abstract |
| </h2> |
| <p> |
| Woe is me. |
| </p> |
| |
| <h2> |
| 2. What the standard says |
| </h2> |
| |
| |
| <h2> |
| 3. Problems with "C" ctype : global locales, termination. |
| </h2> |
| |
| <p> |
| 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. |
| </p> |
| |
| <h2> |
| 4. Design |
| </h2> |
| The two required specializations are implemented as follows: |
| |
| <p> |
| <code> |
| ctype<char> |
| </code> |
| </p> |
| <p> |
| This is simple specialization. Implementing this was a piece of cake. |
| </p> |
| |
| <p> |
| <code> |
| ctype<wchar_t> |
| </code> |
| </p> |
| <p> |
| 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. |
| </p> |
| |
| <p> |
| Neither of these two required specializations deals with Unicode |
| characters. As such, libstdc++-v3 implements |
| </p> |
| |
| <h2> |
| 5. Examples |
| </h2> |
| |
| <pre> |
| typedef ctype<char> cctype; |
| </pre> |
| |
| More information can be found in the following testcases: |
| <ul> |
| <li> testsuite/22_locale/ctype_char_members.cc </li> |
| <li> testsuite/22_locale/ctype_wchar_t_members.cc </li> |
| </ul> |
| |
| <h2> |
| 6. Unresolved Issues |
| </h2> |
| |
| <ul> |
| <li> how to deal with the global locale issue? </li> |
| |
| <li> how to deal with different types than char, wchar_t? </li> |
| |
| <li> codecvt/ctype overlap: narrow/widen </li> |
| |
| <li> mask typedef in codecvt_base, argument types in codecvt. |
| what is know about this type? </li> |
| |
| <li> why mask* argument in codecvt? </li> |
| |
| <li> 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? </li> |
| |
| <li> 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> </li> |
| |
| <li> rename abstract base class. See if just smash-overriding |
| is a better approach. Clarify, add sanity to naming. </li> |
| |
| </ul> |
| |
| |
| <h2> |
| 7. Acknowledgments |
| </h2> |
| Ulrich Drepper for patient answering of late-night questions, skeletal |
| examples, and C language expertise. |
| |
| <h2> |
| 8. Bibliography / Referenced Documents |
| </h2> |
| |
| Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters "6. Character Set Handling" and "7 Locales and Internationalization" |
| |
| <p> |
| Drepper, Ulrich, Numerous, late-night email correspondence |
| </p> |
| |
| <p> |
| ISO/IEC 14882:1998 Programming languages - C++ |
| </p> |
| |
| <p> |
| ISO/IEC 9899:1999 Programming languages - C |
| </p> |
| |
| <p> |
| Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000 |
| </p> |
| |
| <p> |
| Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000 |
| </p> |
| |
| <p> |
| 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 |
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