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1 | <?xml version="1.0" encoding="utf-8"?> |
2 | <!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN" | |
3 | "http://www.boost.org/tools/boostbook/dtd/boostbook.dtd"> | |
4 | <library name="Array" dirname="array" id="array" last-revision="$Date$"> | |
5 | <libraryinfo> | |
6 | <author> | |
7 | <firstname>Nicolai</firstname> | |
8 | <surname>Josuttis</surname> | |
9 | </author> | |
10 | ||
11 | <copyright> | |
12 | <year>2001</year> | |
13 | <year>2002</year> | |
14 | <year>2003</year> | |
15 | <year>2004</year> | |
16 | <holder>Nicolai M. Josuttis</holder> | |
17 | </copyright> | |
18 | ||
19 | <legalnotice> | |
20 | <para>Distributed under the Boost Software License, Version 1.0. | |
21 | (See accompanying file <filename>LICENSE_1_0.txt</filename> or copy at | |
22 | <ulink | |
23 | url="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</ulink>) | |
24 | </para> | |
25 | </legalnotice> | |
26 | ||
27 | <librarypurpose>STL compliant container wrapper for arrays of constant size</librarypurpose> | |
28 | <librarycategory name="category:containers"/> | |
29 | </libraryinfo> | |
30 | ||
31 | <title>Boost.Array</title> | |
32 | ||
33 | <section id="array.intro"> | |
34 | <title>Introduction</title> | |
35 | ||
36 | <using-namespace name="boost"/> | |
37 | <using-class name="array"/> | |
38 | ||
39 | <para>The C++ Standard Template Library STL as part of the C++ | |
40 | Standard Library provides a framework for processing algorithms on | |
41 | different kind of containers. However, ordinary arrays don't | |
42 | provide the interface of STL containers (although, they provide | |
43 | the iterator interface of STL containers).</para> | |
44 | ||
45 | <para>As replacement for ordinary arrays, the STL provides class | |
46 | <code><classname>std::vector</classname></code>. However, | |
47 | <code><classname>std::vector<></classname></code> provides | |
48 | the semantics of dynamic arrays. Thus, it manages data to be able | |
49 | to change the number of elements. This results in some overhead in | |
50 | case only arrays with static size are needed.</para> | |
51 | ||
52 | <para>In his book, <emphasis>Generic Programming and the | |
53 | STL</emphasis>, Matthew H. Austern introduces a useful wrapper | |
54 | class for ordinary arrays with static size, called | |
55 | <code>block</code>. It is safer and has no worse performance than | |
56 | ordinary arrays. In <emphasis>The C++ Programming | |
57 | Language</emphasis>, 3rd edition, Bjarne Stroustrup introduces a | |
58 | similar class, called <code>c_array</code>, which I (<ulink | |
59 | url="http://www.josuttis.com">Nicolai Josuttis</ulink>) present | |
60 | slightly modified in my book <emphasis>The C++ Standard Library - | |
61 | A Tutorial and Reference</emphasis>, called | |
62 | <code>carray</code>. This is the essence of these approaches | |
63 | spiced with many feedback from <ulink | |
64 | url="http://www.boost.org">boost</ulink>.</para> | |
65 | ||
66 | <para>After considering different names, we decided to name this | |
67 | class simply <code><classname>array</classname></code>.</para> | |
68 | ||
69 | <para>Note that this class is suggested to be part of the next | |
70 | Technical Report, which will extend the C++ Standard (see | |
71 | <ulink url="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1548.htm">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</ulink>).</para> | |
72 | ||
73 | <para>Update: <code>std::array</code> is (as of C++11) part of the C++ standard. | |
74 | The differences between <code>boost::array</code> and <code>std::array</code> are minimal. | |
75 | If you are using C++11, you should consider using <code>std::array</code> instead of <code>boost::array</code>. | |
76 | </para> | |
77 | ||
78 | <para>Class <code><classname>array</classname></code> fulfills most | |
79 | but not all of the requirements of "reversible containers" (see | |
80 | Section 23.1, [lib.container.requirements] of the C++ | |
81 | Standard). The reasons array is not an reversible STL container is | |
82 | because: | |
83 | <itemizedlist spacing="compact"> | |
84 | <listitem><simpara>No constructors are provided.</simpara></listitem> | |
85 | <listitem><simpara>Elements may have an undetermined initial value (see <xref linkend="array.rationale"/>).</simpara></listitem> | |
86 | <listitem><simpara><functionname>swap</functionname>() has no constant complexity.</simpara></listitem> | |
87 | <listitem><simpara><methodname>size</methodname>() is always constant, based on the second template argument of the type.</simpara></listitem> | |
88 | <listitem><simpara>The container provides no allocator support.</simpara></listitem> | |
89 | </itemizedlist> | |
90 | </para> | |
91 | ||
92 | <para>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that: | |
93 | <itemizedlist spacing="compact"> | |
94 | <listitem><simpara><methodname>front</methodname>() and <methodname>back</methodname>() are provided.</simpara></listitem> | |
95 | <listitem><simpara><methodname>operator[]</methodname> and <methodname>at</methodname>() are provided.</simpara></listitem> | |
96 | </itemizedlist> | |
97 | </para> | |
98 | </section> | |
99 | ||
100 | <library-reference> | |
101 | <header name="boost/array.hpp"> | |
102 | <namespace name="boost"> | |
103 | <class name="array"> | |
104 | <template> | |
105 | <template-type-parameter name="T"/> | |
106 | <template-nontype-parameter name="N"> | |
107 | <type>std::size_t</type> | |
108 | </template-nontype-parameter> | |
109 | </template> | |
110 | ||
111 | <purpose><para>STL compliant container wrapper for arrays of constant size</para></purpose> | |
112 | <typedef name="value_type"> | |
113 | <type>T</type> | |
114 | </typedef> | |
115 | <typedef name="iterator"> | |
116 | <type>T*</type> | |
117 | </typedef> | |
118 | <typedef name="const_iterator"> | |
119 | <type>const T*</type> | |
120 | </typedef> | |
121 | <typedef name="reverse_iterator"> | |
122 | <type><classname>std::reverse_iterator</classname><iterator></type> | |
123 | </typedef> | |
124 | <typedef name="const_reverse_iterator"> | |
125 | <type><classname>std::reverse_iterator</classname><const_iterator></type> | |
126 | </typedef> | |
127 | <typedef name="reference"> | |
128 | <type>T&</type> | |
129 | </typedef> | |
130 | <typedef name="const_reference"> | |
131 | <type>const T&</type> | |
132 | </typedef> | |
133 | <typedef name="size_type"> | |
134 | <type>std::size_t</type> | |
135 | </typedef> | |
136 | <typedef name="difference_type"> | |
137 | <type>std::ptrdiff_t</type> | |
138 | </typedef> | |
139 | ||
140 | <static-constant name="static_size"> | |
141 | <type>size_type</type> | |
142 | <default>N</default> | |
143 | </static-constant> | |
144 | ||
145 | <copy-assignment> | |
146 | <template> | |
147 | <template-type-parameter name="U"/> | |
148 | </template> | |
149 | <parameter name="other"> | |
150 | <paramtype>const <classname>array</classname><U, N>&</paramtype> | |
151 | </parameter> | |
152 | <effects><simpara><code>std::copy(rhs.<methodname>begin</methodname>(),rhs.<methodname>end</methodname>(), <methodname>begin</methodname>())</code></simpara></effects> | |
153 | </copy-assignment> | |
154 | ||
155 | <method-group name="iterator support"> | |
156 | <overloaded-method name="begin"> | |
157 | <signature> | |
158 | <type>iterator</type> | |
159 | </signature> | |
160 | <signature cv="const"> | |
161 | <type>const_iterator</type> | |
162 | </signature> | |
163 | ||
164 | <returns><simpara>iterator for the first element</simpara></returns> | |
165 | <throws><simpara>will not throw</simpara></throws> | |
166 | </overloaded-method> | |
167 | ||
168 | <overloaded-method name="end"> | |
169 | <signature> | |
170 | <type>iterator</type> | |
171 | </signature> | |
172 | <signature cv="const"> | |
173 | <type>const_iterator</type> | |
174 | </signature> | |
175 | ||
176 | <returns><simpara>iterator for position after the last element</simpara></returns> | |
177 | <throws><simpara>will not throw</simpara></throws> | |
178 | </overloaded-method> | |
179 | </method-group> | |
180 | ||
181 | <method-group name="reverse iterator support"> | |
182 | <overloaded-method name="rbegin"> | |
183 | <signature> | |
184 | <type>reverse_iterator</type> | |
185 | </signature> | |
186 | <signature cv="const"> | |
187 | <type>const_reverse_iterator</type> | |
188 | </signature> | |
189 | ||
190 | <returns><simpara>reverse iterator for the first element of reverse iteration</simpara></returns> | |
191 | </overloaded-method> | |
192 | ||
193 | <overloaded-method name="rend"> | |
194 | <signature> | |
195 | <type>reverse_iterator</type> | |
196 | </signature> | |
197 | <signature cv="const"> | |
198 | <type>const_reverse_iterator</type> | |
199 | </signature> | |
200 | ||
201 | <returns><simpara>reverse iterator for position after the last element in reverse iteration</simpara></returns> | |
202 | </overloaded-method> | |
203 | </method-group> | |
204 | ||
205 | <method-group name="capacity"> | |
206 | <method name="size"> | |
207 | <type>size_type</type> | |
208 | <returns><simpara><code>N</code></simpara></returns> | |
209 | </method> | |
210 | <method name="empty"> | |
211 | <type>bool</type> | |
212 | <returns><simpara><code>N==0</code></simpara></returns> | |
213 | <throws><simpara>will not throw</simpara></throws> | |
214 | </method> | |
215 | <method name="max_size"> | |
216 | <type>size_type</type> | |
217 | <returns><simpara><code>N</code></simpara></returns> | |
218 | <throws><simpara>will not throw</simpara></throws> | |
219 | </method> | |
220 | </method-group> | |
221 | ||
222 | <method-group name="element access"> | |
223 | <overloaded-method name="operator[]"> | |
224 | <signature> | |
225 | <type>reference</type> | |
226 | <parameter name="i"> | |
227 | <paramtype>size_type</paramtype> | |
228 | </parameter> | |
229 | </signature> | |
230 | ||
231 | <signature cv="const"> | |
232 | <type>const_reference</type> | |
233 | <parameter name="i"> | |
234 | <paramtype>size_type</paramtype> | |
235 | </parameter> | |
236 | </signature> | |
237 | ||
238 | <requires><simpara><code>i < N</code></simpara></requires> | |
239 | <returns><simpara>element with index <code>i</code></simpara></returns> | |
240 | <throws><simpara>will not throw.</simpara></throws> | |
241 | </overloaded-method> | |
242 | ||
243 | <overloaded-method name="at"> | |
244 | <signature> | |
245 | <type>reference</type> | |
246 | <parameter name="i"> | |
247 | <paramtype>size_type</paramtype> | |
248 | </parameter> | |
249 | </signature> | |
250 | ||
251 | <signature cv="const"> | |
252 | <type>const_reference</type> | |
253 | <parameter name="i"> | |
254 | <paramtype>size_type</paramtype> | |
255 | </parameter> | |
256 | </signature> | |
257 | ||
258 | <returns><simpara>element with index <code>i</code></simpara></returns> | |
259 | <throws><simpara><code><classname>std::range_error</classname></code> if <code>i >= N</code></simpara></throws> | |
260 | </overloaded-method> | |
261 | ||
262 | <overloaded-method name="front"> | |
263 | <signature> | |
264 | <type>reference</type> | |
265 | </signature> | |
266 | <signature cv="const"> | |
267 | <type>const_reference</type> | |
268 | </signature> | |
269 | <requires><simpara><code>N > 0</code></simpara></requires> | |
270 | <returns><simpara>the first element</simpara></returns> | |
271 | <throws><simpara>will not throw</simpara></throws> | |
272 | </overloaded-method> | |
273 | ||
274 | <overloaded-method name="back"> | |
275 | <signature> | |
276 | <type>reference</type> | |
277 | </signature> | |
278 | <signature cv="const"> | |
279 | <type>const_reference</type> | |
280 | </signature> | |
281 | <requires><simpara><code>N > 0</code></simpara></requires> | |
282 | <returns><simpara>the last element</simpara></returns> | |
283 | <throws><simpara>will not throw</simpara></throws> | |
284 | </overloaded-method> | |
285 | ||
286 | <method name="data" cv="const"> | |
287 | <type>const T*</type> | |
288 | <returns><simpara><code>elems</code></simpara></returns> | |
289 | <throws><simpara>will not throw</simpara></throws> | |
290 | </method> | |
291 | ||
292 | <method name="c_array"> | |
293 | <type>T*</type> | |
294 | <returns><simpara><code>elems</code></simpara></returns> | |
295 | <throws><simpara>will not throw</simpara></throws> | |
296 | </method> | |
297 | </method-group> | |
298 | ||
299 | <method-group name="modifiers"> | |
300 | <method name="swap"> | |
301 | <type>void</type> | |
302 | <parameter name="other"> | |
303 | <paramtype><classname>array</classname><T, N>&</paramtype> | |
304 | </parameter> | |
305 | <effects><simpara><code>std::swap_ranges(<methodname>begin</methodname>(), <methodname>end</methodname>(), other.<methodname>begin</methodname>())</code></simpara></effects> | |
306 | <complexity><simpara>linear in <code>N</code></simpara></complexity> | |
307 | </method> | |
308 | <method name="assign"> | |
309 | <type>void</type> | |
310 | <parameter name="value"> | |
311 | <paramtype>const T&</paramtype> | |
312 | </parameter> | |
313 | <effects><simpara><code>std::fill_n(<methodname>begin</methodname>(), N, value)</code></simpara></effects> | |
314 | </method> | |
315 | </method-group> | |
316 | ||
317 | <data-member name="elems[N]"> <!-- HACK --> | |
318 | <type>T</type> | |
319 | </data-member> | |
320 | ||
321 | <free-function-group name="specialized algorithms"> | |
322 | <function name="swap"> | |
323 | <template> | |
324 | <template-type-parameter name="T"/> | |
325 | <template-nontype-parameter name="N"> | |
326 | <type>std::size_t</type> | |
327 | </template-nontype-parameter> | |
328 | </template> | |
329 | ||
330 | <type>void</type> | |
331 | ||
332 | <parameter name="x"> | |
333 | <paramtype><classname>array</classname><T, N>&</paramtype> | |
334 | </parameter> | |
335 | <parameter name="y"> | |
336 | <paramtype><classname>array</classname><T, N>&</paramtype> | |
337 | </parameter> | |
338 | ||
339 | <effects><simpara><code>x.<methodname>swap</methodname>(y)</code></simpara></effects> | |
340 | <throws><simpara>will not throw.</simpara></throws> | |
341 | </function> | |
342 | </free-function-group> | |
343 | ||
344 | <free-function-group name="comparisons"> | |
345 | <function name="operator=="> | |
346 | <template> | |
347 | <template-type-parameter name="T"/> | |
348 | <template-nontype-parameter name="N"> | |
349 | <type>std::size_t</type> | |
350 | </template-nontype-parameter> | |
351 | </template> | |
352 | ||
353 | <type>bool</type> | |
354 | ||
355 | <parameter name="x"> | |
356 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
357 | </parameter> | |
358 | <parameter name="y"> | |
359 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
360 | </parameter> | |
361 | ||
362 | <returns><simpara><code>std::equal(x.<methodname>begin</methodname>(), x.<methodname>end</methodname>(), y.<methodname>begin</methodname>())</code></simpara> | |
363 | </returns> | |
364 | </function> | |
365 | ||
366 | <function name="operator!="> | |
367 | <template> | |
368 | <template-type-parameter name="T"/> | |
369 | <template-nontype-parameter name="N"> | |
370 | <type>std::size_t</type> | |
371 | </template-nontype-parameter> | |
372 | </template> | |
373 | ||
374 | <type>bool</type> | |
375 | ||
376 | <parameter name="x"> | |
377 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
378 | </parameter> | |
379 | <parameter name="y"> | |
380 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
381 | </parameter> | |
382 | ||
383 | <returns><simpara><code>!(x == y)</code></simpara> | |
384 | </returns> | |
385 | </function> | |
386 | ||
387 | <function name="operator<"> | |
388 | <template> | |
389 | <template-type-parameter name="T"/> | |
390 | <template-nontype-parameter name="N"> | |
391 | <type>std::size_t</type> | |
392 | </template-nontype-parameter> | |
393 | </template> | |
394 | ||
395 | <type>bool</type> | |
396 | ||
397 | <parameter name="x"> | |
398 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
399 | </parameter> | |
400 | <parameter name="y"> | |
401 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
402 | </parameter> | |
403 | ||
404 | <returns><simpara><code>std::lexicographical_compare(x.<methodname>begin</methodname>(), x.<methodname>end</methodname>(), y.<methodname>begin</methodname>(), y.<methodname>end</methodname>())</code></simpara> | |
405 | </returns> | |
406 | </function> | |
407 | ||
408 | <function name="operator>"> | |
409 | <template> | |
410 | <template-type-parameter name="T"/> | |
411 | <template-nontype-parameter name="N"> | |
412 | <type>std::size_t</type> | |
413 | </template-nontype-parameter> | |
414 | </template> | |
415 | ||
416 | <type>bool</type> | |
417 | ||
418 | <parameter name="x"> | |
419 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
420 | </parameter> | |
421 | <parameter name="y"> | |
422 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
423 | </parameter> | |
424 | ||
425 | <returns><simpara><code>y < x</code></simpara></returns> | |
426 | </function> | |
427 | ||
428 | <function name="operator<="> | |
429 | <template> | |
430 | <template-type-parameter name="T"/> | |
431 | <template-nontype-parameter name="N"> | |
432 | <type>std::size_t</type> | |
433 | </template-nontype-parameter> | |
434 | </template> | |
435 | ||
436 | <type>bool</type> | |
437 | ||
438 | <parameter name="x"> | |
439 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
440 | </parameter> | |
441 | <parameter name="y"> | |
442 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
443 | </parameter> | |
444 | ||
445 | <returns><simpara><code>!(y < x)</code></simpara></returns> | |
446 | </function> | |
447 | ||
448 | <function name="operator>="> | |
449 | <template> | |
450 | <template-type-parameter name="T"/> | |
451 | <template-nontype-parameter name="N"> | |
452 | <type>std::size_t</type> | |
453 | </template-nontype-parameter> | |
454 | </template> | |
455 | ||
456 | <type>bool</type> | |
457 | ||
458 | <parameter name="x"> | |
459 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
460 | </parameter> | |
461 | <parameter name="y"> | |
462 | <paramtype>const <classname>array</classname><T, N>&</paramtype> | |
463 | </parameter> | |
464 | ||
465 | <returns><simpara><code>!(x < y)</code></simpara></returns> | |
466 | </function> | |
467 | </free-function-group> | |
468 | </class> | |
469 | </namespace> | |
470 | </header> | |
471 | </library-reference> | |
472 | ||
473 | <section id="array.rationale"> | |
474 | <title>Design Rationale</title> | |
475 | ||
476 | <para>There was an important design tradeoff regarding the | |
477 | constructors: We could implement array as an "aggregate" (see | |
478 | Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would | |
479 | mean: | |
480 | <itemizedlist> | |
481 | <listitem><simpara>An array can be initialized with a | |
482 | brace-enclosing, comma-separated list of initializers for the | |
483 | elements of the container, written in increasing subscript | |
484 | order:</simpara> | |
485 | ||
486 | <programlisting><classname>boost::array</classname><int,4> a = { { 1, 2, 3 } };</programlisting> | |
487 | ||
488 | <simpara>Note that if there are fewer elements in the | |
489 | initializer list, then each remaining element gets | |
490 | default-initialized (thus, it has a defined value).</simpara> | |
491 | </listitem></itemizedlist></para> | |
492 | ||
493 | <para>However, this approach has its drawbacks: <emphasis | |
494 | role="bold"> passing no initializer list means that the elements | |
495 | have an indetermined initial value</emphasis>, because the rule says | |
496 | that aggregates may have: | |
497 | <itemizedlist> | |
498 | <listitem><simpara>No user-declared constructors.</simpara></listitem> | |
499 | <listitem><simpara>No private or protected non-static data members.</simpara></listitem> | |
500 | <listitem><simpara>No base classes.</simpara></listitem> | |
501 | <listitem><simpara>No virtual functions.</simpara></listitem> | |
502 | </itemizedlist> | |
503 | </para> | |
504 | ||
505 | <para>Nevertheless, The current implementation uses this approach.</para> | |
506 | ||
507 | <para>Note that for standard conforming compilers it is possible to | |
508 | use fewer braces (according to 8.5.1 (11) of the Standard). That is, | |
509 | you can initialize an array as follows:</para> | |
510 | ||
511 | <programlisting> | |
512 | <classname>boost::array</classname><int,4> a = { 1, 2, 3 }; | |
513 | </programlisting> | |
514 | ||
515 | <para>I'd appreciate any constructive feedback. <emphasis | |
516 | role="bold">Please note: I don't have time to read all boost | |
517 | mails. Thus, to make sure that feedback arrives to me, please send | |
518 | me a copy of each mail regarding this class.</emphasis></para> | |
519 | ||
520 | <para>The code is provided "as is" without expressed or implied | |
521 | warranty.</para> | |
522 | ||
523 | </section> | |
524 | ||
525 | <section id="array.more.info"> | |
526 | <title>For more information...</title> | |
527 | <para>To find more details about using ordinary arrays in C++ and | |
528 | the framework of the STL, see e.g. | |
529 | ||
530 | <literallayout>The C++ Standard Library - A Tutorial and Reference | |
531 | by Nicolai M. Josuttis | |
532 | Addison Wesley Longman, 1999 | |
533 | ISBN 0-201-37926-0</literallayout> | |
534 | </para> | |
535 | ||
536 | <para><ulink url="http://www.josuttis.com/">Home Page of Nicolai | |
537 | Josuttis</ulink></para> | |
538 | </section> | |
539 | ||
540 | <section id="array.ack"> | |
541 | <title>Acknowledgements</title> | |
542 | ||
543 | <para>Doug Gregor ported the documentation to the BoostBook format.</para> | |
544 | </section> | |
545 | ||
546 | <!-- Notes: | |
547 | empty() should return N != 0 | |
548 | size(), empty(), max_size() should be const | |
549 | --> | |
550 | ||
551 | </library> |