1<HTML> 2<!-- 3 Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000 4 5 Distributed under the Boost Software License, Version 1.0. 6 (See accompanying file LICENSE_1_0.txt or copy at 7 http://www.boost.org/LICENSE_1_0.txt) 8 --> 9<Head> 10<Title>Vector Property Map</Title> 11<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" 12 ALINK="#ff0000"> 13<IMG SRC="../../../boost.png" 14 ALT="C++ Boost" width="277" height="86"> 15 16<BR Clear> 17 18 19<H2><A NAME="sec:vector-property-map"></A> 20</h2> 21<PRE> 22template<typename T, typename IndexMap = identity_property_map> 23class vector_property_map; 24</PRE> 25 26<P> 27This property map is used to efficiently store properties for a variable 28number of elements. It's somewhere between <a 29href="associative_property_map.html">associative_property_map</a> and 30<a href="iterator_property_map.html">iterator_property_map</a>. The latter 31is very fast, but requires that the number of stored elements is known 32when creating property map. The former does not have this requirement, but 33is slower, and requires stored elements to be comparable. 34 35<p> 36The <tt>vector_property_map</tt> uses mapping from key to indices, 37and allows to add new elements. It accomplishes this by storing values 38in a vector, which is resized on demand. 39 40<p> 41Note that <tt>vector_property_map</tt> does not provide reference/pointer 42stability for stored values. 43 44<h3>Example</h3> 45 46<a href="../example/example3.cpp">example3.cpp</a>: 47 48<p> 49<pre> 50#include <boost/property_map/vector_property_map.hpp> 51#include <string> 52#include <iostream> 53 54int main() 55{ 56 boost::vector_property_map<std::string> m; 57 58 // Assign string to '4'. 59 m[4] = "e"; 60 std::cout << "'" << m[4] << "'\n"; 61 62 // Grab string from '10'. Since none is associated, 63 // "" will be returned. 64 std::cout << "'" << m[10] << "'\n"; 65} 66</pre> 67 68<H3>Where Defined</H3> 69 70<P> 71<a href="../../../boost/property_map/vector_property_map.hpp"><TT>boost/property_map/vector_property_map.hpp</TT></a> 72 73<p> 74<H3>Model Of</H3> 75 76<a href="./LvaluePropertyMap.html">Lvalue Property Map</a> 77 78<P> 79 80<H3>Template Parameters</H3> 81 82<P> 83 84<TABLE border> 85<TR> 86<th>Parameter</th><th>Description</th><th>Default</th> 87</tr> 88 89 90<TR> 91<TD><TT>T</TT></TD> 92<TD>The type of property value. Must be both <a 93href="http://www.sgi.com/tech/stl/Assignable.html">Assignable</a> 94and <a 95href="http://www.sgi.com/tech/stl/DefaultConstructible.html">DefaultConstructible</a>. 96</TD> 97<TD> </td> 98</tr> 99 100<TR> 101<TD><TT>IndexMap</TT></TD> <TD>Must be a model of <a 102href="./ReadablePropertyMap.html">Readable Property Map</a> 103and the value type must be convertible to 104<tt>std::vector<T>::size_type</tt>.</TD> 105<TD><a href="identity_property_map.html">identity_property_map</a></TD> 106</TR> 107 108</TABLE> 109<P> 110 111<H3>Members</H3> 112 113<P> 114In addition to the methods and functions required by <a 115href="./LvaluePropertyMap.html">Lvalue Property Map</a>, this 116class has the following members. 117 118<hr> 119 120<pre> 121vector_property_map(const IndexMap& index = IndexMap()) 122</pre> 123Constructor which takes an index map. 124 125<hr> 126 127<pre> 128vector_property_map(unsigned initial_size, const IndexMap& index = IndexMap()) 129</pre> 130This constructor version allows to specify maximum index of element 131that will be stored. Correct number will improve performance, but semantic 132is always the same. 133 134<hr> 135 136<pre> 137vector_property_map(const vector_property_map&) 138</pre> 139Copy constructor. The copy will share the same data and changes 140made to it will affect original property map. 141 142<hr> 143 144<pre> 145vector_property_map& operator=(const vector_property_map&) 146</pre> 147Assignment operator. The semantic is the same as for copy constructor. 148 149<hr> 150 151<pre> 152reference operator[](const key_type& v) const 153</pre> 154The operator bracket for property access. 155 156<hr> 157 158<pre> 159std::vector<T>::iterator storage_begin() 160std::vector<T>::iterator storage_end() 161std::vector<T>::const_iterator storage_begin() 162std::vector<T>::const_iterator storage_end() 163</pre> 164 165<p>This group of methods gives access to begin and end iterators of the 166underlying vector.</p> 167 168<p><b>Rationale:</b> The methods are handy, for example, when it's needed to 169specify a single value for all elements in a freshly created property map. The 170methods are not called simply "begin" and "end" since 171conceptually, <tt>vector_property_map</tt> is unbounded map, and has no end 172iterator. The direct access to the underlying method is not provided, since 173it would decrease encapsulation and make future performance tuning dangerous. 174 175<p><b>Acknolegements:</b> Matthias Troyer suggested adding those functions. 176 177<hr> 178 179<pre> 180void reserve(unsigned size) 181</pre> 182Reserve the space for storing elements with maximum index of 'size'. Unless 183element with greater index is accesses, all accesses will be take O(1) time. 184 185 186<hr> 187 188<h3>Non-Member functions</h3> 189 190<hr> 191 192<pre> 193template<typename T, typename IndexMap> 194vector_property_map<T, IndexMap> 195make_vector_property_map(IndexMap index) 196{ 197 return vector_property_map<T, IndexMap>(index); 198} 199</pre> 200A function for conveniently creating a vector property map. 201 202<br> 203<HR> 204<TABLE> 205<TR valign=top> 206<TD nowrap>Copyright © 2002</TD><TD> 207<a HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</a>, 208Indiana University (<A 209HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br> 210<A HREF="http://www.boost.org/people/liequan_lee.htm">Lie-Quan Lee</A>, Indiana University (<A HREF="mailto:llee1@osl.iu.edu">llee1@osl.iu.edu</A>)<br> 211<A HREF="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</A>, 212Indiana University (<A 213HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) 214</TD></TR> 215<tr> 216<td nowrap>Copyright © 2003</td><td>Vladimir Prus</td> 217</tr> 218</TABLE> 219 220</BODY> 221</HTML> 222
