1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
|
<HTML>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!-- Created on October, 7 2003 by texi2html 1.64 -->
<!--
Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author)
Karl Berry <karl@freefriends.org>
Olaf Bachmann <obachman@mathematik.uni-kl.de>
and many others.
Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>
Send bugs and suggestions to <texi2html@mathematik.uni-kl.de>
-->
<HEAD>
<TITLE>The Ada95 XML Library: The Unicode module</TITLE>
<META NAME="description" CONTENT="The Ada95 XML Library: The Unicode module">
<META NAME="keywords" CONTENT="The Ada95 XML Library: The Unicode module">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<META NAME="Generator" CONTENT="texi2html 1.64">
</HEAD>
<BODY LANG="" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#800080" ALINK="#FF0000">
<A NAME="SEC2"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_1.html#SEC1"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC3"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H1> 2. The Unicode module </H1>
<!--docid::SEC2::-->
<P>
Unicode provides a unique number for every character, no matter what the
platform, no matter what the program, no matter what the language.
</P><P>
Fundamentally, computers just deal with numbers. They store letters and
other characters by assigning a number for each one. Before Unicode was
invented, there were hundreds of different encoding systems for
assigning these numbers. No single encoding could contain enough
characters: for example, the European Union alone requires several
different encodings to cover all its languages. Even for a single
language like English no single encoding was adequate for all the
letters, punctuation, and technical symbols in common use.
</P><P>
These encoding systems also conflict with one another. That is, two
encodings can use the same number for two different characters, or use
different numbers for the same character. Any given computer (especially
servers) needs to support many different encodings; yet whenever data is
passed between different encodings or platforms, that data always runs
the risk of corruption.
</P><P>
Unicode provides a unique number for every character, no matter what the
platform, no matter what the program, no matter what the language. The
Unicode Standard has been adopted by such industry leaders as Apple, HP,
IBM, JustSystem, Microsoft, Oracle, SAP, Sun, Sybase, Unisys and many
others. Unicode is required by modern standards such as XML, Java,
ECMAScript (JavaScript), LDAP, CORBA 3.0, WML, etc., and is the official
way to implement ISO/IEC 10646. It is supported in many operating
systems, all modern browsers, and many other products. The emergence of
the Unicode Standard, and the availability of tools supporting it, are
among the most significant recent global software technology trends.
</P><P>
The following sections explain the basic vocabulary and concepts
associated with Unicode and encodings.
</P><P>
Most of the information comes from the official Unicode Web site, at
<A HREF="http://www.unicode.org/unicode/reports/tr17">http://www.unicode.org/unicode/reports/tr17</A>.
</P><P>
Part of this documentation comes from <A HREF="http://www.unicode.org">http://www.unicode.org</A>, the
official web site for Unicode.
</P><P>
Some information was also extracted from the "UTF-8 and Unicode FAQ"
by M. Kuhn, available at <A HREF="???">???</A>.
</P><P>
<BLOCKQUOTE><TABLE BORDER=0 CELLSPACING=0>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="xml_2.html#SEC3">2.1 Glyphs</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="xml_2.html#SEC4">2.2 Repertoires and subsets</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="xml_2.html#SEC5">2.3 Character sets</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="xml_2.html#SEC6">2.4 Character encoding schemes</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="xml_2.html#SEC7">2.5 Misc. functions</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
</TABLE></BLOCKQUOTE>
<P>
<A NAME="Glyphs"></A>
<HR SIZE="6">
<A NAME="SEC3"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC4"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 2.1 Glyphs </H2>
<!--docid::SEC3::-->
<P>
A glyph is a particular representation of a character or part of a
character.
</P><P>
Several representations are possible, mostly depending on the exact font
used at that time. A single glyph can correspond to a sequence of characters,
or a single character to a sequence of glyphs.
</P><P>
The Unicode standard doesn't deal with glyphs, although a suggested
representation is given for each character in the standard. Likewise, this
module doesn't provide any graphical support for Unicode, and will just
deal with textual memory representation and encodings.
</P><P>
Take a look at the <B>GtkAda</B> library that provides the graphical interface
for unicode in the upcoming 2.0 version.
</P><P>
<A NAME="Repertoires and subsets"></A>
<HR SIZE="6">
<A NAME="SEC4"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC3"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC5"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC5"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 2.2 Repertoires and subsets </H2>
<!--docid::SEC4::-->
<P>
A repertoire is a set of abstract characters to be encoded, normally
a familiar alphabet or symbol set. For instance, the alphabet used to
spell English words, or the one used for the Russian alphabet are two
such repertoires.
</P><P>
There exist two types of repertoires, close and open ones. The former
is the most common one, and the two examples above are such repertoires.
No character is ever added to them.
</P><P>
Unicode is also a repertoire, but an open one. New entries are
added to it. However, it is guaranteed that none will ever be deleted from it.
Unicode intends to be a universal repertoire, with all possible
characters currently used in the world. It currently contains all the
alphabets, including a number of alphabets associated with dead languages
like hieroglyphs. It also contains a number of often used symbols, like
mathematical signs.
</P><P>
The goal of this Unicode module is to convert all characters to entries in
the Unicode repertoire, so that any applications can communicate with each
other in a portable manner.
</P><P>
Given its size, most applications will only support a subset of Unicode.
Some of the scripts, most notably Arabic and Asian languages, require a
special support in the application (right-to-left writing,...), and thus will
not be supported by some applications.
</P><P>
The Unicode standard includes a set of internal catalogs, called
collections. Each character in these collections is given a special name,
in addition to its code, to improve readability.
</P><P>
Several child packages (<B>Unicode.Names.*</B>) define those names. For
instance:
</P><P>
<DL COMPACT>
<DT><B>Unicode.Names.Basic_Latin</B>
<DD>This contains the basic characters used in most western European languages,
including the standard ASCII subset.
<P>
<DT><B>Unicode.Names.Cyrillic</B>
<DD>This contains the Russian alphabet.
<P>
<DT><B>Unicode.Names.Mathematical_Operators</B>
<DD>This contains several mathematical symbols
</DL>
<P>
More than 80 such packages exist.
</P><P>
<A NAME="Character sets"></A>
<HR SIZE="6">
<A NAME="SEC5"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC4"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC6"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC6"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 2.3 Character sets </H2>
<!--docid::SEC5::-->
<P>
A character set is a mapping from a set of abstract characters to some
non-negative integers. The integer associated with a character is called
its code point, and the character itself is called the encoded character.
</P><P>
There exist a number of standard character sets, unfortunately not compatible
with each other. For instance, ASCII is one of these character sets, and
contains 128 characters. A super-set of it is the ISO/8859-1 character set.
Another character set is the JIS X 0208, used to encode Japanese characters.
</P><P>
Note that a character set is different from a repertoire. For instance, the
same character C with cedilla doesn't have the same integer value in the
ISO/8859-1 character set and the ISO/8859-1 character set.
</P><P>
Unicode is also such a character set, that contains all the possible
characters and associate a standard integer with them. A similar and
fully compatible character set is ISO/10646. The only addition that Unicode
does other ISO/10646 is that it also specifies algorithms for rendering
presentation forms of some scripts (say Arabic), handling of bi-directional
texts that mix for instance Latin and Hebrew, algorithms for sorting and
string comparison, and much more.
</P><P>
Currently, our Unicode package doesn't include any support for these
algorithms.
</P><P>
Unicode and ISO 10646 define formally a 31-bit character set. However,
of this huge code space, so far characters have been assigned only to
the first 65534 positions (0x0000 to 0xFFFD). The characters that are
expected to be encoded outside the 16-bit range belong all to rather
exotic scripts (e.g., Hieroglyphics) that are only used by specialists
for historic and scientific purposes
</P><P>
The Unicode module contains a set of packages to provide conversion from some
of the most common character sets to and from Unicode. These are the
<B>Unicode.CCS.*</B> packages.
</P><P>
All these packages have a common structure:
</P><P>
<OL>
<LI>They define a global variable of type <CODE>Character_Set</CODE> with two
fields, ie the two conversion functions between the given character set and
Unicode.
<P>
These functions convert one character (actually its code point) at a time.
</P><P>
<LI>They also define a number of standard names associated with this
character set. For instance, the ISO/8859-1 set is also known as Latin1.
<P>
The function <CODE>Unicode.CCS.Get_Character_Set</CODE> can be used to find a
character set by its standard name.
</OL>
<P>
Currently, the following sets are supported:
<DL COMPACT>
<DT><B>ISO/8859-1 aka Latin1</B>
<DD>This is the standard character set used to represent most Western
European languages including: Albanian, Catalan, Danish, Dutch, English,
Faroese, Finnish, French, Galician, German, Irish, Icelandic, Italian,
Norwegian, Portuguese, Spanish and Swedish.
<P>
<DT><B>ISO/8859-2 aka Latin2</B>
<DD>This character set supports the Slavic languages of Central Europe
which use the Latin alphabet. The ISO-8859-2 set is used for the following
languages: Czech, Croat, German, Hungarian, Polish, Romanian, Slovak and
Slovenian.
<P>
<DT><B>ISO/8859-3</B>
<DD>This character set is used for Esperanto, Galician, Maltese and Turkish
<P>
<DT><B>ISO/8859-4</B>
<DD>Some letters were added to the ISO-8859-4 to support languages such as
Estonian, Latvian and Lithuanian. It is an incomplete precursor of the
Latin 6 set.
<P>
</DL>
<P>
<A NAME="Character encoding schemes"></A>
<HR SIZE="6">
<A NAME="SEC6"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC5"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC7"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC7"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 2.4 Character encoding schemes </H2>
<!--docid::SEC6::-->
<P>
We now know how each encoded character can be represented by an integer
value (code point) depending on the character set.
</P><P>
Character encoding schemes deal with the representation of a sequence
of integers to a sequence of code units. A code unit is a sequence of
bytes on a computer architecture.
</P><P>
There exists a number of possible encoding schemes. Some of them encode
all integers on the same number of bytes. They are called fixed-width
encoding forms, and include the standard encoding for Internet emails
(<B>7bits</B>, but it can't encode all characters), as well as the simple
<B>8bits</B> scheme, or the <B>EBCDIC</B> scheme. Among them is also the
<B>UTF-32</B> scheme which is defined in the Unicode standard.
</P><P>
Another set of encoding schemes encode integers on a variable number of
bytes. These include two schemes that are also defined in the Unicode
standard, namely <B>Utf-8</B> and <B>Utf-16</B>.
</P><P>
Unicode doesn't impose any specific encoding. However, it is most often
associated with one of the Utf encodings. They each have their own
properties and advantages:
</P><P>
<DL COMPACT>
<DT><B>Utf32</B>
<DD>This is the simplest of all these encodings. It simply encodes all the
characters on 32 bits (4 bytes). This encodes all the possible characters
in Unicode, and is obviously straightforward to manipulate. However, given
that the first 65535 characters in Unicode are enough to encode all known
languages currently in use, Utf32 is also a waste of space in most cases.
<P>
<DT><B>Utf16</B>
<DD>For the above reason, Utf16 was defined. Most characters are only encoded
on two bytes (which is enough for the first 65535 and most current
characters). In addition, a number of special code points have been
defined, known as <I>surrogate pairs</I>, that make the encoding of integers
greater than 65535 possible. The integers are then encoded on four bytes.
As a result, Utf16 is thus much more memory-efficient and requires less
space than Utf32 to encode sequences of characters. However, it is also
more complex to decode.
<P>
<DT><B>Utf8</B>
<DD>This is an even more space-efficient encoding, but is also more complex
to decode. More important, it is compatible with the most currently used
simple 8bit encoding.
<P>
Utf8 has the following properties:
<UL>
<LI>Characters 0 to 127 (ASCII) are encoded simply as a single byte.
This means that files and strings which contain only 7-bit ASCII
characters have the same encoding under both ASCII and UTF-8.
<P>
<LI>Characters greater than 127 are encoded as a sequence of several
bytes, each of which has the most significant bit set. Therefore,
no ASCII byte can appear as part of any other character.
<P>
<LI>The first byte of a multibyte sequence that represents a non-ASCII
character is always in the range 0xC0 to 0xFD and it indicates how
many bytes follow for this character. All further bytes in a
multibyte sequence are in the range 0x80 to 0xBF. This allows easy
resynchronization and makes the encoding stateless and robust
against missing bytes.
<P>
<LI>UTF-8 encoded characters may theoretically be up to six bytes
long, however the first 16-bit characters are only up to three bytes
long.
<P>
</UL>
<P>
</DL>
<P>
Note that the encodings above, except for Utf8, have two versions, depending
on the chosen byte order on the machine.
</P><P>
The Ada95 Unicode module provides a set of packages that provide an easy
conversion between all the encoding schemes, as well as basic manipulations
of these byte sequences. These are the <B>Unicode.CES.*</B> packages.
Currently, four encoding schemes are supported, the three Utf schemes and
the basic 8bit encoding which corresponds to the standard Ada strings.
</P><P>
It also supports some routines to convert from one byte-order to another.
</P><P>
The following examples show a possible use of these packages:
</P><P>
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>Converting a latin1 string coded on 8 bits to a Utf8 latin2 file
involves the following steps:
Latin1 string (bytes associated with code points in Latin1)
| "use Unicode.CES.Basic_8bit.To_Utf32"
v
Utf32 latin1 string (contains code points in Latin1)
| "Convert argument to To_Utf32 should be
v Unicode.CCS.Iso_8859_1.Convert"
Utf32 Unicode string (contains code points in Unicode)
| "use Unicode.CES.Utf8.From_Utf32"
v
Utf8 Unicode string (contains code points in Unicode)
| "Convert argument to From_Utf32 should be
v Unicode.CCS.Iso_8859_2.Convert"
Utf8 Latin2 string (contains code points in Latin2)
</FONT></pre></td></tr></table></P><P>
<A NAME="Misc. functions"></A>
<HR SIZE="6">
<A NAME="SEC7"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC6"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 2.5 Misc. functions </H2>
<!--docid::SEC7::-->
<P>
The package <B>Unicode</B> contains a series of <CODE>Is_*</CODE> functions,
matching the Unicode standard.
</P><P>
<DL COMPACT>
<DT><B>Is_White_Space</B>
<DD>Return True if the character argument is a space character, ie a space,
horizontal tab, line feed or carriage return.
<P>
<DT><B>Is_Letter</B>
<DD>Return True if the character argument is a letter. This includes the
standard English letters, as well as some less current cases defined in the
standard.
<P>
<DT><B>Is_Base_Char</B>
<DD>Return True if the character is a base character, ie a character whose
meaning can be modified with a combining character.
<P>
<DT><B>Is_Digit</B>
<DD>Return True if the character is a digit (numeric character)
<P>
<DT><B>Is_Combining_Char</B>
<DD>Return True if the character is a combining character. Combining characters
are accents or other diacritical marks that are added to the previous
character.
<P>
The most important accented characters, like those used in the
orthographies of common languages, have codes of their own in Unicode to
ensure backwards compatibility with older character sets. Accented
characters that have their own code position, but could also be
represented as a pair of another character followed by a combining
character, are known as precomposed characters. Precomposed characters
are available in Unicode for backwards compatibility with older encodings
such as ISO 8859 that had no combining characters. The combining
character mechanism allows to add accents and other diacritical marks to
any character
</P><P>
Note however that your application must provide specific support for
combining characters, at least if you want to represent them visually.
</P><P>
<DT><B>Is_Extender</B>
<DD>True if Char is an extender character.
<P>
<DT><B>Is_Ideographic</B>
<DD>True if Char is an ideographic character. This is defined only for
Asian languages.
<P>
</DL>
<P>
<A NAME="The Input module"></A>
<HR SIZE="6">
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_2.html#SEC2"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_3.html#SEC8"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[Index]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="xml_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<BR>
<FONT SIZE="-1">
This document was generated
by <I>Emmanuel Briot</I> on <I>October, 7 2003</I>
using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html
"><I>texi2html</I></A>
</BODY>
</HTML>
|
