ICU-3650 Move some stuff from the readme.html to the User's Guide.
X-SVN-Rev: 15036
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George Rhoten
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@ -80,11 +80,6 @@
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<li><a href="#ImportantNotesCPlusPlus">Using ICU in a Multithreaded
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Environment</a></li>
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<li><a href="#CharStrings">char * strings in ICU</a></li>
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<li><a href="#ImportantNotesDefaultCP">Using the Default
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Codepage</a></li>
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<li><a href="#ImportantNotesWindows">Windows Platform</a></li>
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<li><a href="#ImportantNotesUNIX">UNIX Type Platforms</a></li>
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@ -1628,305 +1623,6 @@ del common/libicuuc.so
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<a href=
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"http://docs.sun.com/db/doc/806-6867/6jfpgdcob?a=view">http://docs.sun.com/db/doc/806-6867/6jfpgdcob?a=view</a></p>
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<h3><a name="CharStrings" href="#CharStrings" id="CharStrings">char *
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strings in ICU</a></h3>
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<p>The C/C++ languages do not provide a portable way to specify Unicode
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code point or string literals other than with arrays of numeric constants.
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For convenience, ICU4C tends to use char * strings in places where only
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"invariant characters" (a portable subset of the 7-bit ASCII repertoire)
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are used. This allows locale IDs, charset names, resource bundle item keys
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and similar items to be easily specified as string literals in the source
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code. The same types of strings are also stored as "invariant character"
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char * strings in the ICU data files.</p>
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<p>ICU has hard coded mapping tables in <code>source/common/putil.c</code>
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to convert invariant characters to and from Unicode without using a full
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ICU converter. These tables must match the encoding of string literals in
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the ICU code as well as in the ICU data files.</p>
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<p><strong>Important:</strong> ICU assumes that at least the invariant
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characters always have the same codes as is common on platforms with the
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same charset family (ASCII vs. EBCDIC). <em>ICU has not been tested on
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platforms where this is not the case.</em></p>
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<p>Some usage of char * strings in ICU assumes the system charset instead
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of invariant characters. Such strings are only handled with the default
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converter (See the following section). The system charset is usually a
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superset of the invariant characters.</p>
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<p>The following are the ASCII and EBCDIC byte values for all of the
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invariant characters (see also unicode/utypes.h):</p>
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<table border="1" summary=
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"There are a few invariant characters that can be used for char * strings">
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<tr>
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<th>Character(s)</th>
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<th>ASCII</th>
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<th>EBCDIC</th>
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</tr>
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<tr>
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<td>a..i</td>
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<td>61..69</td>
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<td>81..89</td>
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</tr>
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<tr>
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<td>j..r</td>
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<td>6A..72</td>
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<td>91..99</td>
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</tr>
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<tr>
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<td>s..z</td>
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<td>73..7A</td>
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<td>A2..A9</td>
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</tr>
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<tr>
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<td>A..I</td>
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<td>41..49</td>
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<td>C1..C9</td>
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</tr>
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<tr>
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<td>J..R</td>
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<td>4A..52</td>
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<td>D1..D9</td>
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</tr>
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<tr>
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<td>S..Z</td>
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<td>53..5A</td>
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<td>E2..E9</td>
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</tr>
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<tr>
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<td>0..9</td>
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<td>30..39</td>
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<td>F0..F9</td>
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</tr>
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<tr>
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<td>(space)</td>
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<td>20</td>
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<td>40</td>
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</tr>
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<tr>
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<td>"</td>
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<td>22</td>
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<td>7F</td>
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</tr>
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<tr>
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<td>%</td>
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<td>25</td>
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<td>6C</td>
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</tr>
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<tr>
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<td>&</td>
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<td>26</td>
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<td>50</td>
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</tr>
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<tr>
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<td>'</td>
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<td>27</td>
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<td>7D</td>
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</tr>
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<tr>
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<td>(</td>
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<td>28</td>
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<td>4D</td>
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</tr>
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<tr>
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<td>)</td>
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<td>29</td>
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<td>5D</td>
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</tr>
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<tr>
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<td>*</td>
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<td>2A</td>
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<td>5C</td>
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</tr>
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<tr>
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<td>+</td>
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<td>2B</td>
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<td>4E</td>
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</tr>
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<tr>
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<td>,</td>
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<td>2C</td>
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<td>6B</td>
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</tr>
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<tr>
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<td>-</td>
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<td>2D</td>
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<td>60</td>
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</tr>
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<tr>
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<td>.</td>
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<td>2E</td>
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<td>4B</td>
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</tr>
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<tr>
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<td>/</td>
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<td>2F</td>
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<td>61</td>
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</tr>
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<tr>
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<td>:</td>
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<td>3A</td>
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<td>7A</td>
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</tr>
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<tr>
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<td>;</td>
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<td>3B</td>
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<td>5E</td>
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</tr>
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<tr>
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<td><</td>
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<td>3C</td>
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<td>4C</td>
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</tr>
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<tr>
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<td>=</td>
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<td>3D</td>
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<td>7E</td>
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</tr>
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<tr>
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<td>></td>
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<td>3E</td>
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<td>6E</td>
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</tr>
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<tr>
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<td>?</td>
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<td>3F</td>
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<td>6F</td>
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</tr>
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<tr>
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<td>_</td>
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<td>5F</td>
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<td>6D</td>
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</tr>
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</table>
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<h3><a name="ImportantNotesDefaultCP" href="#ImportantNotesDefaultCP" id=
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"ImportantNotesDefaultCP">Using the default codepage</a></h3>
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<p>ICU has code to determine the default codepage of the system or process.
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This default codepage can be used to convert <code>char *</code> strings to
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and from Unicode.</p>
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<p>Depending on system design, setup and APIs, it may not always be
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possible to find a default codepage that fully works as expected. For
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example,</p>
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<ul>
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<li>On Windows there are three encodings in use at the same time. Unicode
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(UTF-16) is always used inside of Windows, while for <code>char *</code>
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encodings there are two classes, called "ANSI" and "OEM" codepages. ICU
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will use the ANSI codepage. Note that the OEM codepage is used by default
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for console window output.</li>
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<li>On some UNIX-type systems, non-standard names are used for encodings,
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or non-standard encodings are used altogether. Although ICU supports over
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200 encodings in its standard build and many more aliases for them, it
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will not be able to recognize such non-standard names.</li>
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<li>Some systems do not have a notion of a system or process codepage,
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and may not have APIs for that.</li>
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</ul>
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<p>If you have means of detecting a default codepage name that are more
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appropriate for your application, then you should set that name with
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<code>ucnv_setDefaultName()</code> as the first ICU function call. This
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makes sure that the internally cached default converter will be
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instantiated from your preferred name.</p>
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<p>Starting in ICU 2.0, when a converter for the default codepage cannot be
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opened, a fallback default codepage name and converter will be used. On
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most platforms, this will be US-ASCII. For z/OS (OS/390), ibm-1047-s390 is
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the default fallback codepage. For AS/400 (iSeries), ibm-37 is the default
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fallback codepage. This default fallback codepage is used when the
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operating system is using a non-standard name for a default codepage, or
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the converter was not packaged with ICU. The feature allows ICU to run in
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unusual computing environments without completely failing.</p>
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<h3><a name="ImportantNotesWindows" href="#ImportantNotesWindows" id=
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"ImportantNotesWindows">Windows Platform</a></h3>
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