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jlechner |
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<meta name="AUTHOR" content="bkoz@redhat.com (Benjamin Kosnik)" />
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<meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL" />
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<meta name="DESCRIPTION" content="Notes on the ctype implementation." />
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<title>Notes on the ctype implementation.</title>
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</head>
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<body>
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<h1>
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Notes on the ctype implementation.
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</h1>
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<em>
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prepared by Benjamin Kosnik (bkoz@redhat.com) on August 30, 2000
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</em>
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<h2>
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1. Abstract
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</h2>
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<p>
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Woe is me.
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</p>
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<h2>
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2. What the standard says
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</h2>
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<h2>
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3. Problems with "C" ctype : global locales, termination.
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</h2>
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<p>
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For the required specialization codecvt<wchar_t, char, mbstate_t> ,
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conversions are made between the internal character set (always UCS4
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on GNU/Linux) and whatever the currently selected locale for the
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LC_CTYPE category implements.
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</p>
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<h2>
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4. Design
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</h2>
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The two required specializations are implemented as follows:
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<p>
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<code>
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ctype<char>
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</code>
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</p>
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<p>
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This is simple specialization. Implementing this was a piece of cake.
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</p>
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<p>
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<code>
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ctype<wchar_t>
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</code>
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</p>
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<p>
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This specialization, by specifying all the template parameters, pretty
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much ties the hands of implementors. As such, the implementation is
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straightforward, involving mcsrtombs for the conversions between char
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to wchar_t and wcsrtombs for conversions between wchar_t and char.
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</p>
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<p>
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Neither of these two required specializations deals with Unicode
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characters. As such, libstdc++-v3 implements
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</p>
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<h2>
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5. Examples
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</h2>
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<pre>
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typedef ctype<char> cctype;
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</pre>
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More information can be found in the following testcases:
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<ul>
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<li> testsuite/22_locale/ctype_char_members.cc </li>
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<li> testsuite/22_locale/ctype_wchar_t_members.cc </li>
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</ul>
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<h2>
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6. Unresolved Issues
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</h2>
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<ul>
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<li> how to deal with the global locale issue? </li>
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<li> how to deal with different types than char, wchar_t? </li>
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<li> codecvt/ctype overlap: narrow/widen </li>
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<li> mask typedef in codecvt_base, argument types in codecvt.
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what is know about this type? </li>
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<li> why mask* argument in codecvt? </li>
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<li> can this be made (more) generic? is there a simple way to
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straighten out the configure-time mess that is a by-product of
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this class? </li>
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<li> get the ctype<wchar_t>::mask stuff under control. Need to
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make some kind of static table, and not do lookup evertime
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somebody hits the do_is... functions. Too bad we can't just
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redefine mask for ctype<wchar_t> </li>
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<li> rename abstract base class. See if just smash-overriding
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is a better approach. Clarify, add sanity to naming. </li>
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</ul>
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<h2>
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7. Acknowledgments
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</h2>
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Ulrich Drepper for patient answering of late-night questions, skeletal
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examples, and C language expertise.
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<h2>
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8. Bibliography / Referenced Documents
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</h2>
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Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters "6. Character Set Handling" and "7 Locales and Internationalization"
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<p>
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Drepper, Ulrich, Numerous, late-night email correspondence
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</p>
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<p>
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ISO/IEC 14882:1998 Programming languages - C++
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</p>
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<p>
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ISO/IEC 9899:1999 Programming languages - C
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</p>
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<p>
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Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000
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</p>
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<p>
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Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000
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</p>
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<p>
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System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x)
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The Open Group/The Institute of Electrical and Electronics Engineers, Inc.
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http://www.opennc.org/austin/docreg.html
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</p>
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</body>
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