1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>is_empty</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. Geometry"> 8<link rel="up" href="../algorithms.html" title="Algorithms"> 9<link rel="prev" href="intersects/intersects_2_two_geometries.html" title="intersects (two geometries)"> 10<link rel="next" href="is_simple.html" title="is_simple"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="intersects/intersects_2_two_geometries.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../algorithms.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="is_simple.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="geometry.reference.algorithms.is_empty"></a><a class="link" href="is_empty.html" title="is_empty">is_empty</a> 28</h4></div></div></div> 29<p> 30 <a class="indexterm" name="idm45635695086208"></a> 31Checks if a geometry is the empty set. 32 </p> 33<h6> 34<a name="geometry.reference.algorithms.is_empty.h0"></a> 35 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.synopsis"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.synopsis">Synopsis</a> 36 </h6> 37<p> 38</p> 39<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Geometry</span><span class="special">></span> 40<span class="keyword">bool</span> <span class="identifier">is_empty</span><span class="special">(</span><span class="identifier">Geometry</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">geometry</span><span class="special">)</span></pre> 41<p> 42 </p> 43<h6> 44<a name="geometry.reference.algorithms.is_empty.h1"></a> 45 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.parameters"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.parameters">Parameters</a> 46 </h6> 47<div class="informaltable"><table class="table"> 48<colgroup> 49<col> 50<col> 51<col> 52<col> 53</colgroup> 54<thead><tr> 55<th> 56 <p> 57 Type 58 </p> 59 </th> 60<th> 61 <p> 62 Concept 63 </p> 64 </th> 65<th> 66 <p> 67 Name 68 </p> 69 </th> 70<th> 71 <p> 72 Description 73 </p> 74 </th> 75</tr></thead> 76<tbody><tr> 77<td> 78 <p> 79 Geometry const & 80 </p> 81 </td> 82<td> 83 <p> 84 Any type fulfilling a Geometry Concept 85 </p> 86 </td> 87<td> 88 <p> 89 geometry 90 </p> 91 </td> 92<td> 93 <p> 94 A model of the specified concept 95 </p> 96 </td> 97</tr></tbody> 98</table></div> 99<h6> 100<a name="geometry.reference.algorithms.is_empty.h2"></a> 101 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.returns"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.returns">Returns</a> 102 </h6> 103<p> 104 Returns true if the geometry is the empty set 105 </p> 106<h6> 107<a name="geometry.reference.algorithms.is_empty.h3"></a> 108 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.header"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.header">Header</a> 109 </h6> 110<p> 111 Either 112 </p> 113<p> 114 <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 115 </p> 116<p> 117 Or 118 </p> 119<p> 120 <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">algorithms</span><span class="special">/</span><span class="identifier">is_empty</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 121 </p> 122<h6> 123<a name="geometry.reference.algorithms.is_empty.h4"></a> 124 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.conformance"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.conformance">Conformance</a> 125 </h6> 126<p> 127 The function is_empty implements function IsEmpty from the <a href="http://www.opengeospatial.org/standards/sfa" target="_top">OGC 128 Simple Feature Specification</a>. 129 </p> 130<h6> 131<a name="geometry.reference.algorithms.is_empty.h5"></a> 132 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.supported_geometries"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.supported_geometries">Supported 133 geometries</a> 134 </h6> 135<div class="informaltable"><table class="table"> 136<colgroup> 137<col> 138<col> 139</colgroup> 140<thead><tr> 141<th> 142 <p> 143 Geometry 144 </p> 145 </th> 146<th> 147 <p> 148 Status 149 </p> 150 </th> 151</tr></thead> 152<tbody> 153<tr> 154<td> 155 <p> 156 Point 157 </p> 158 </td> 159<td> 160 <p> 161 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 162 </p> 163 </td> 164</tr> 165<tr> 166<td> 167 <p> 168 Segment 169 </p> 170 </td> 171<td> 172 <p> 173 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 174 </p> 175 </td> 176</tr> 177<tr> 178<td> 179 <p> 180 Box 181 </p> 182 </td> 183<td> 184 <p> 185 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 186 </p> 187 </td> 188</tr> 189<tr> 190<td> 191 <p> 192 Linestring 193 </p> 194 </td> 195<td> 196 <p> 197 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 198 </p> 199 </td> 200</tr> 201<tr> 202<td> 203 <p> 204 Ring 205 </p> 206 </td> 207<td> 208 <p> 209 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 210 </p> 211 </td> 212</tr> 213<tr> 214<td> 215 <p> 216 Polygon 217 </p> 218 </td> 219<td> 220 <p> 221 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 222 </p> 223 </td> 224</tr> 225<tr> 226<td> 227 <p> 228 MultiPoint 229 </p> 230 </td> 231<td> 232 <p> 233 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 234 </p> 235 </td> 236</tr> 237<tr> 238<td> 239 <p> 240 MultiLinestring 241 </p> 242 </td> 243<td> 244 <p> 245 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 246 </p> 247 </td> 248</tr> 249<tr> 250<td> 251 <p> 252 MultiPolygon 253 </p> 254 </td> 255<td> 256 <p> 257 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 258 </p> 259 </td> 260</tr> 261<tr> 262<td> 263 <p> 264 Variant 265 </p> 266 </td> 267<td> 268 <p> 269 <span class="inlinemediaobject"><img src="../../../img/ok.png" alt="ok"></span> 270 </p> 271 </td> 272</tr> 273</tbody> 274</table></div> 275<h6> 276<a name="geometry.reference.algorithms.is_empty.h6"></a> 277 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.complexity"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.complexity">Complexity</a> 278 </h6> 279<p> 280 Constant-time 281 </p> 282<h6> 283<a name="geometry.reference.algorithms.is_empty.h7"></a> 284 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.example"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.example">Example</a> 285 </h6> 286<p> 287 Check if a geometry is the empty set 288 </p> 289<p> 290</p> 291<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 292 293<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 294<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">point_xy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 295 296 297<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 298<span class="special">{</span> 299 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">multi_linestring</span> 300 <span class="special"><</span> 301 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">linestring</span> 302 <span class="special"><</span> 303 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">d2</span><span class="special">::</span><span class="identifier">point_xy</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> 304 <span class="special">></span> 305 <span class="special">></span> <span class="identifier">mls</span><span class="special">;</span> 306 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span><span class="string">"MULTILINESTRING((0 0,0 10,10 0),(1 1,8 1,1 8))"</span><span class="special">,</span> <span class="identifier">mls</span><span class="special">);</span> 307 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Is empty? "</span> <span class="special"><<</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">is_empty</span><span class="special">(</span><span class="identifier">mls</span><span class="special">)</span> <span class="special">?</span> <span class="string">"yes"</span> <span class="special">:</span> <span class="string">"no"</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 308 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">clear</span><span class="special">(</span><span class="identifier">mls</span><span class="special">);</span> 309 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Is empty (after clearing)? "</span> <span class="special"><<</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">is_empty</span><span class="special">(</span><span class="identifier">mls</span><span class="special">)</span> <span class="special">?</span> <span class="string">"yes"</span> <span class="special">:</span> <span class="string">"no"</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 310 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 311<span class="special">}</span> 312</pre> 313<p> 314 </p> 315<p> 316 Output: 317 </p> 318<pre class="programlisting">Is empty? no 319Is empty (after clearing)? yes 320</pre> 321<h6> 322<a name="geometry.reference.algorithms.is_empty.h8"></a> 323 <span class="phrase"><a name="geometry.reference.algorithms.is_empty.see_also"></a></span><a class="link" href="is_empty.html#geometry.reference.algorithms.is_empty.see_also">See 324 also</a> 325 </h6> 326<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 327 <a class="link" href="num_points.html" title="num_points">num_points</a> 328 </li></ul></div> 329</div> 330<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 331<td align="left"></td> 332<td align="right"><div class="copyright-footer">Copyright © 2009-2019 Barend Gehrels, Bruno Lalande, Mateusz Loskot, Adam 333 Wulkiewicz, Oracle and/or its affiliates<p> 334 Distributed under the Boost Software License, Version 1.0. (See accompanying 335 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>) 336 </p> 337</div></td> 338</tr></table> 339<hr> 340<div class="spirit-nav"> 341<a accesskey="p" href="intersects/intersects_2_two_geometries.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../algorithms.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="is_simple.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 342</div> 343</body> 344</html> 345
