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  21   <h1>
  22   Notes on the ctype implementation.
  23   </h1>
  24 <em>
  25 prepared by Benjamin Kosnik (bkoz@redhat.com) on August 30, 2000
  26 </em>
  27
  28 <h2>
  29 1. Abstract
  30 </h2>
  31 <p>
  32 Woe is me.
  33 </p>
  34
  35 <h2>
  36 2. What the standard says
  37 </h2>
  38
  39
  40 <h2>
  41 3. Problems with &quot;C&quot; ctype : global locales, termination.
  42 </h2>
  43
  44 <p>
  45 For the required specialization codecvt&lt;wchar_t, char, mbstate_t&gt; ,
  46 conversions are made between the internal character set (always UCS4
  47 on GNU/Linux) and whatever the currently selected locale for the
  48 LC_CTYPE category implements.
  49 </p>
  50
  51 <h2>
  52 4. Design
  53 </h2>
  54 The two required specializations are implemented as follows:
  55
  56 <p>
  57 <code>
  58 ctype&lt;char&gt;
  59 </code>
  60 </p>
  61 <p>
  62 This is simple specialization. Implementing this was a piece of cake.
  63 </p>
  64
  65 <p>
  66 <code>
  67 ctype&lt;wchar_t&gt;
  68 </code>
  69 </p>
  70 <p>
  71 This specialization, by specifying all the template parameters, pretty
  72 much ties the hands of implementors. As such, the implementation is
  73 straightforward, involving mcsrtombs for the conversions between char
  74 to wchar_t and wcsrtombs for conversions between wchar_t and char.
  75 </p>
  76
  77 <p>
  78 Neither of these two required specializations deals with Unicode
  79 characters. As such, libstdc++-v3 implements
  80 </p>
  81
  82 <h2>
  83 5.  Examples
  84 </h2>
  85
  86 <pre>
  87   typedef ctype&lt;char&gt; cctype;
  88 </pre>
  89
  90 More information can be found in the following testcases:
  91 <ul>
  92 <li> testsuite/22_locale/ctype_char_members.cc    </li>
  93 <li> testsuite/22_locale/ctype_wchar_t_members.cc </li>
  94 </ul>
  95
  96 <h2>
  97 6.  Unresolved Issues
  98 </h2>
  99
 100 <ul>
 101    <li> how to deal with the global locale issue? </li>
 102
 103    <li> how to deal with different types than char, wchar_t? </li>
 104
 105    <li> codecvt/ctype overlap: narrow/widen </li>
 106
 107    <li> mask typedef in codecvt_base, argument types in codecvt.
 108    what is know about this type? </li>
 109
 110    <li> why mask* argument in codecvt? </li>
 111
 112    <li> can this be made (more) generic? is there a simple way to
 113    straighten out the configure-time mess that is a by-product of
 114    this class? </li>
 115
 116    <li> get the ctype&lt;wchar_t&gt;::mask stuff under control. Need to
 117    make some kind of static table, and not do lookup evertime
 118    somebody hits the do_is... functions. Too bad we can't just
 119    redefine mask for ctype&lt;wchar_t&gt; </li>
 120
 121    <li> rename abstract base class. See if just smash-overriding
 122    is a better approach. Clarify, add sanity to naming. </li>
 123
 124 </ul>
 125
 126
 127 <h2>
 128 7. Acknowledgments
 129 </h2>
 130 Ulrich Drepper for patient answering of late-night questions, skeletal
 131 examples, and C language expertise.
 132
 133 <h2>
 134 8. Bibliography / Referenced Documents
 135 </h2>
 136
 137 Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters &quot;6. Character Set Handling&quot; and &quot;7 Locales and Internationalization&quot;
 138
 139 <p>
 140 Drepper, Ulrich, Numerous, late-night email correspondence
 141 </p>
 142
 143 <p>
 144 ISO/IEC 14882:1998 Programming languages - C++
 145 </p>
 146
 147 <p>
 148 ISO/IEC 9899:1999 Programming languages - C
 149 </p>
 150
 151 <p>
 152 Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000
 153 </p>
 154
 155 <p>
 156 Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000
 157 </p>
 158
 159 <p>
 160 System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x)
 161 The Open Group/The Institute of Electrical and Electronics Engineers, Inc.
 162 http://www.opennc.org/austin/docreg.html
 163 </p>
 164
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