1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Element iteration</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. 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Iteration over 110 segments is fast, compared to an iteration over elements, particularly if 111 intervals are large. But if we want to view our interval containers as containers 112 of elements that are usable with std::algoritms, we need to iterate over 113 elements. 114 </p> 115<p> 116 Iteration over elements . . . 117 </p> 118<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 119<li class="listitem"> 120 is possible only for integral or discrete <code class="computeroutput"><span class="identifier">domain_types</span></code> 121 </li> 122<li class="listitem"> 123 can be very <span class="emphasis"><em><span class="bold"><strong>slow</strong></span></em></span> 124 if the intervals are very large. 125 </li> 126<li class="listitem"> 127 and is therefore <span class="emphasis"><em><span class="bold"><strong>depreciated</strong></span></em></span> 128 </li> 129</ul></div> 130<p> 131 On the other hand, sometimes iteration over interval containers on the element 132 level might be desired, if you have some interface that works for <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">SortedAssociativeContainers</span></code> 133 of elements and you need to quickly use it with an interval container. Accepting 134 the poorer performance might be less bothersome at times than adjusting your 135 whole interface for segment iteration. 136 </p> 137<div class="caution"><table border="0" summary="Caution"> 138<tr> 139<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../doc/src/images/caution.png"></td> 140<th align="left">Caution</th> 141</tr> 142<tr><td align="left" valign="top"><p> 143 So we advice you to choose element iteration over interval containers 144 <span class="emphasis"><em><span class="bold"><strong>judiciously</strong></span></em></span>. Do not 145 use element iteration <span class="emphasis"><em><span class="bold"><strong>by default or habitual</strong></span></em></span>. 146 Always try to achieve results using member functions, global functions 147 or operators (preferably inplace versions) or iteration over segments first. 148 </p></td></tr> 149</table></div> 150<div class="informaltable"><table class="table"> 151<colgroup> 152<col> 153<col> 154<col> 155</colgroup> 156<thead><tr> 157<th> 158 <p> 159 <span class="emphasis"><em><span class="bold"><strong>Synopsis Complexities</strong></span></em></span> 160 </p> 161 </th> 162<th> 163 <p> 164 interval<br> sets 165 </p> 166 </th> 167<th> 168 <p> 169 interval<br> maps 170 </p> 171 </th> 172</tr></thead> 173<tbody> 174<tr> 175<td> 176 <p> 177 <code class="computeroutput"><span class="identifier">J</span> <span class="identifier">elements_begin</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span></code> 178 </p> 179 </td> 180<td> 181 <p> 182 <span class="emphasis"><em>O(1)</em></span> 183 </p> 184 </td> 185<td> 186 <p> 187 <span class="emphasis"><em>O(1)</em></span> 188 </p> 189 </td> 190</tr> 191<tr> 192<td> 193 <p> 194 <code class="computeroutput"><span class="identifier">J</span> <span class="identifier">elements_end</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span></code> 195 </p> 196 </td> 197<td> 198 <p> 199 <span class="emphasis"><em>O(1)</em></span> 200 </p> 201 </td> 202<td> 203 <p> 204 <span class="emphasis"><em>O(1)</em></span> 205 </p> 206 </td> 207</tr> 208<tr> 209<td> 210 <p> 211 <code class="computeroutput"><span class="identifier">J</span> <span class="identifier">elements_rbegin</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span></code> 212 </p> 213 </td> 214<td> 215 <p> 216 <span class="emphasis"><em>O(1)</em></span> 217 </p> 218 </td> 219<td> 220 <p> 221 <span class="emphasis"><em>O(1)</em></span> 222 </p> 223 </td> 224</tr> 225<tr> 226<td> 227 <p> 228 <code class="computeroutput"><span class="identifier">J</span> <span class="identifier">elements_rend</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span></code> 229 </p> 230 </td> 231<td> 232 <p> 233 <span class="emphasis"><em>O(1)</em></span> 234 </p> 235 </td> 236<td> 237 <p> 238 <span class="emphasis"><em>O(1)</em></span> 239 </p> 240 </td> 241</tr> 242</tbody> 243</table></div> 244<div class="informaltable"><table class="table"> 245<colgroup> 246<col> 247<col> 248</colgroup> 249<thead><tr> 250<th> 251 <p> 252 <span class="emphasis"><em><span class="bold"><strong>Element iteration</strong></span></em></span> 253 </p> 254 </th> 255<th> 256 <p> 257 Description 258 </p> 259 </th> 260</tr></thead> 261<tbody> 262<tr> 263<td> 264 <p> 265</p> 266<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"> <span class="identifier">element_iterator</span> <span class="identifier">elements_begin</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span> 267<span class="identifier">element_const_iterator</span> <span class="identifier">elements_begin</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&)</span></pre> 268<p> 269 </p> 270 </td> 271<td> 272 <p> 273 Returns an element iterator to the first element of the container. 274 </p> 275 </td> 276</tr> 277<tr> 278<td> 279 <p> 280</p> 281<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"> <span class="identifier">element_iterator</span> <span class="identifier">elements_end</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span> 282<span class="identifier">element_const_iterator</span> <span class="identifier">elements_end</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&)</span></pre> 283<p> 284 </p> 285 </td> 286<td> 287 <p> 288 Returns an element iterator to a position <code class="computeroutput"><span class="identifier">elements_end</span><span class="special">(</span><span class="identifier">c</span><span class="special">)</span></code> after the last element of the 289 container. 290 </p> 291 </td> 292</tr> 293<tr> 294<td> 295 <p> 296</p> 297<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"> <span class="identifier">element_reverse_iterator</span> <span class="identifier">elements_rbegin</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span> 298<span class="identifier">element_const_reverse_iterator</span> <span class="identifier">elements_rbegin</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&)</span></pre> 299<p> 300 </p> 301 </td> 302<td> 303 <p> 304 Returns a reverse element iterator to the last element of the container. 305 </p> 306 </td> 307</tr> 308<tr> 309<td> 310 <p> 311</p> 312<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"> <span class="identifier">element_reverse_iterator</span> <span class="identifier">elements_rend</span><span class="special">(</span><span class="identifier">T</span><span class="special">&)</span> 313<span class="identifier">element_const_reverse_iterator</span> <span class="identifier">elements_rend</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&)</span></pre> 314<p> 315 </p> 316 </td> 317<td> 318 <p> 319 Returns a reverse element iterator to a position <code class="computeroutput"><span class="identifier">elements_rend</span><span class="special">(</span><span class="identifier">c</span><span class="special">)</span></code> 320 before the first element of the container. 321 </p> 322 </td> 323</tr> 324</tbody> 325</table></div> 326<p> 327 <span class="emphasis"><em><span class="bold"><strong>Example</strong></span></em></span> 328 </p> 329<p> 330</p> 331<pre class="programlisting"><span class="identifier">interval_set</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">inter_set</span><span class="special">;</span> 332<span class="identifier">inter_set</span><span class="special">.</span><span class="identifier">add</span><span class="special">(</span><span class="identifier">interval</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">right_open</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">3</span><span class="special">))</span> 333 <span class="special">.</span><span class="identifier">add</span><span class="special">(</span><span class="identifier">interval</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">right_open</span><span class="special">(</span><span class="number">7</span><span class="special">,</span><span class="number">9</span><span class="special">));</span> 334 335<span class="keyword">for</span><span class="special">(</span><span class="identifier">interval_set</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">element_const_iterator</span> <span class="identifier">creeper</span> <span class="special">=</span> <span class="identifier">elements_begin</span><span class="special">(</span><span class="identifier">inter_set</span><span class="special">);</span> 336 <span class="identifier">creeper</span> <span class="special">!=</span> <span class="identifier">elements_end</span><span class="special">(</span><span class="identifier">inter_set</span><span class="special">);</span> <span class="special">++</span><span class="identifier">creeper</span><span class="special">)</span> 337 <span class="identifier">cout</span> <span class="special"><<</span> <span class="special">*</span><span class="identifier">creeper</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> 338<span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> 339<span class="comment">//Program output: 0 1 2 7 8</span> 340 341<span class="keyword">for</span><span class="special">(</span><span class="identifier">interval_set</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">element_reverse_iterator</span> <span class="identifier">repeerc</span> <span class="special">=</span> <span class="identifier">elements_rbegin</span><span class="special">(</span><span class="identifier">inter_set</span><span class="special">);</span> 342 <span class="identifier">repeerc</span> <span class="special">!=</span> <span class="identifier">elements_rend</span><span class="special">(</span><span class="identifier">inter_set</span><span class="special">);</span> <span class="special">++</span><span class="identifier">repeerc</span><span class="special">)</span> 343 <span class="identifier">cout</span> <span class="special"><<</span> <span class="special">*</span><span class="identifier">repeerc</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> 344<span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> 345<span class="comment">//Program output: 8 7 2 1 0</span> 346</pre> 347<p> 348 </p> 349<p> 350 <span class="emphasis"><em><span class="bold"><strong>See also . . .</strong></span></em></span> 351 </p> 352<div class="informaltable"><table class="table"> 353<colgroup><col></colgroup> 354<thead><tr></tr></thead> 355<tbody><tr><td> 356 <p> 357 <a class="link" href="iterator_related.html" title="Iterator related"><span class="emphasis"><em><span class="bold"><strong>Segment iteration</strong></span></em></span></a> 358 </p> 359 </td></tr></tbody> 360</table></div> 361<p> 362 <span class="emphasis"><em><span class="bold"><strong>Back to section . . .</strong></span></em></span> 363 </p> 364<div class="informaltable"><table class="table"> 365<colgroup><col></colgroup> 366<thead><tr></tr></thead> 367<tbody> 368<tr><td> 369 <p> 370 <a class="link" href="../interface/function_synopsis.html#function_synopsis_table"><span class="emphasis"><em><span class="bold"><strong>Function 371 Synopsis</strong></span></em></span></a> 372 </p> 373 </td></tr> 374<tr><td> 375 <p> 376 <a class="link" href="../interface.html" title="Interface"><span class="emphasis"><em><span class="bold"><strong>Interface</strong></span></em></span></a> 377 </p> 378 </td></tr> 379</tbody> 380</table></div> 381</div> 382<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 383<td align="left"></td> 384<td align="right"><div class="copyright-footer">Copyright © 2007-2010 Joachim 385 Faulhaber<br>Copyright © 1999-2006 Cortex Software 386 GmbH<p> 387 Distributed under the Boost Software License, Version 1.0. (See accompanying 388 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 389 </p> 390</div></td> 391</tr></table> 392<hr> 393<div class="spirit-nav"> 394<a accesskey="p" href="iterator_related.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../function_reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="streaming__conversion.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 395</div> 396</body> 397</html> 398
