1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>default_allocator</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. Boost.Core"> 8<link rel="up" href="../index.html" title="Chapter 1. Boost.Core"> 9<link rel="prev" href="checked_delete.html" title="checked_delete"> 10<link rel="next" href="demangle.html" title="demangle"> 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="checked_delete.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img 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class="title"> 36<a name="idm45312830116432"></a>Authors</h3></div></div></div> 37<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 38 Glen Fernandes 39 </li></ul></div> 40</div> 41<div class="section"> 42<div class="titlepage"><div><div><h3 class="title"> 43<a name="core.default_allocator.overview"></a><a class="link" href="default_allocator.html#core.default_allocator.overview" title="Overview">Overview</a> 44</h3></div></div></div> 45<p> 46 The header <boost/core/default_allocator.hpp> provides the class template 47 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">default_allocator</span></code> to serve as a minimal 48 default allocator that: 49 </p> 50<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 51<li class="listitem"> 52 Like C++2a's <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code>, does not provide members 53 such as <code class="computeroutput"><span class="identifier">construct</span><span class="special">()</span></code> 54 and <code class="computeroutput"><span class="identifier">destroy</span><span class="special">()</span></code> 55 to be eligible for optimizations by allocator-aware code that detects 56 the absence of these members to provide more optimal construction. 57 </li> 58<li class="listitem"> 59 Supports <code class="computeroutput"><span class="identifier">BOOST_NO_EXCEPTIONS</span></code> 60 in allocation. 61 </li> 62<li class="listitem"> 63 Does not have <code class="computeroutput"><span class="identifier">std</span></code> as 64 an associated namespace. 65 </li> 66</ul></div> 67</div> 68<div class="section"> 69<div class="titlepage"><div><div><h3 class="title"> 70<a name="core.default_allocator.examples"></a><a class="link" href="default_allocator.html#core.default_allocator.examples" title="Examples">Examples</a> 71</h3></div></div></div> 72<p> 73 The following snippet shows the use of this allocator as the default allocator 74 for a container. 75 </p> 76<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Key</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Compare</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special"><</span><span class="identifier">Key</span><span class="special">>,</span> 77 <span class="keyword">class</span> <span class="identifier">Allocator</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">Key</span><span class="special">></span> <span class="special">></span> 78<span class="keyword">class</span> <span class="identifier">FlatSet</span><span class="special">;</span> 79</pre> 80<p> 81 Facilities like <code class="computeroutput"><span class="identifier">make_shared</span></code> 82 can be implemented using <code class="computeroutput"><span class="identifier">allocate_shared</span></code> 83 with <code class="computeroutput"><span class="identifier">default_allocator</span></code>. 84 </p> 85<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> 86<span class="identifier">enable_if_t</span><span class="special"><!</span><span class="identifier">is_array_v</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">></span> 87<span class="identifier">make_shared</span><span class="special">(</span><span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">)</span> 88<span class="special">{</span> 89 <span class="keyword">return</span> <span class="identifier">allocate_shared</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">remove_cv_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">>(),</span> 90 <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...);</span> 91<span class="special">}</span> 92</pre> 93</div> 94<div class="section"> 95<div class="titlepage"><div><div><h3 class="title"> 96<a name="core.default_allocator.reference"></a><a class="link" href="default_allocator.html#core.default_allocator.reference" title="Reference">Reference</a> 97</h3></div></div></div> 98<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 99 100<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 101<span class="keyword">struct</span> <span class="identifier">default_allocator</span> <span class="special">{</span> 102 <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">value_type</span><span class="special">;</span> 103 <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">pointer</span><span class="special">;</span> 104 <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">const_pointer</span><span class="special">;</span> 105 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">add_lvalue_reference_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">reference</span><span class="special">;</span> 106 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">add_lvalue_reference_t</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">const_reference</span><span class="special">;</span> 107 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size_type</span><span class="special">;</span> 108 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ptrdiff_t</span> <span class="identifier">difference_type</span><span class="special">;</span> 109 <span class="keyword">typedef</span> <span class="emphasis"><em>true_type</em></span> <span class="identifier">propagate_on_container_move_assignment</span><span class="special">;</span> 110 <span class="keyword">typedef</span> <span class="emphasis"><em>true_type</em></span> <span class="identifier">is_always_equal</span><span class="special">;</span> 111 112 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> 113 <span class="keyword">struct</span> <span class="identifier">rebind</span> <span class="special">{</span> 114 <span class="keyword">typedef</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">other</span><span class="special">;</span> 115 <span class="special">};</span> 116 117 <span class="keyword">constexpr</span> <span class="identifier">default_allocator</span><span class="special">()</span> <span class="special">=</span> <span class="keyword">default</span><span class="special">;</span> 118 119 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> 120 <span class="keyword">constexpr</span> <span class="identifier">default_allocator</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&)</span> <span class="keyword">noexcept</span> <span class="special">{</span> <span class="special">}</span> 121 122 <span class="keyword">constexpr</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span> 123 <span class="identifier">T</span><span class="special">*</span> <span class="identifier">allocate</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">);</span> 124 <span class="keyword">void</span> <span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">);</span> 125<span class="special">};</span> 126 127<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> 128<span class="keyword">constexpr</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span><span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&,</span> 129 <span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&)</span> <span class="keyword">noexcept</span><span class="special">;</span> 130 131<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> 132<span class="keyword">constexpr</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!=(</span><span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&,</span> 133 <span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&)</span> <span class="keyword">noexcept</span><span class="special">;</span> 134 135<span class="special">}</span> <span class="comment">/* boost */</span> 136</pre> 137<div class="section"> 138<div class="titlepage"><div><div><h4 class="title"> 139<a name="core.default_allocator.reference.members"></a><a class="link" href="default_allocator.html#core.default_allocator.reference.members" title="Members">Members</a> 140</h4></div></div></div> 141<div class="variablelist"> 142<p class="title"><b></b></p> 143<dl class="variablelist"> 144<dt><span class="term"><code class="computeroutput"><span class="keyword">constexpr</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> 145 <span class="identifier">max_size</span><span class="special">()</span> 146 <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code></span></dt> 147<dd><div class="variablelist"> 148<p class="title"><b></b></p> 149<dl class="variablelist"> 150<dt><span class="term">Returns</span></dt> 151<dd><p> 152 The largest value <code class="computeroutput"><span class="identifier">N</span></code> 153 for which the call <code class="computeroutput"><span class="identifier">allocate</span><span class="special">(</span><span class="identifier">N</span><span class="special">)</span></code> might succeed. 154 </p></dd> 155</dl> 156</div></dd> 157<dt><span class="term"><code class="computeroutput"><span class="identifier">T</span><span class="special">*</span> 158 <span class="identifier">allocate</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">);</span></code></span></dt> 159<dd><div class="variablelist"> 160<p class="title"><b></b></p> 161<dl class="variablelist"> 162<dt><span class="term">Returns</span></dt> 163<dd><p> 164 A pointer to the initial element of an array of storage of 165 size <code class="computeroutput"><span class="identifier">n</span> <span class="special">*</span> 166 <span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code>, 167 aligned appropriately for objects of type <code class="computeroutput"><span class="identifier">T</span></code>. 168 </p></dd> 169<dt><span class="term">Remarks</span></dt> 170<dd><p> 171 The storage is obtained by calling <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span> <span class="keyword">new</span></code>. 172 </p></dd> 173<dt><span class="term">Throws</span></dt> 174<dd><p> 175 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_alloc</span></code> if the storage 176 cannot be obtained. 177 </p></dd> 178</dl> 179</div></dd> 180<dt><span class="term"><code class="computeroutput"><span class="keyword">void</span> <span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> 181 <span class="identifier">n</span><span class="special">);</span></code></span></dt> 182<dd><div class="variablelist"> 183<p class="title"><b></b></p> 184<dl class="variablelist"> 185<dt><span class="term">Requires</span></dt> 186<dd><p> 187 <code class="computeroutput"><span class="identifier">p</span></code> shall be 188 a pointer value obtained from <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code>. <code class="computeroutput"><span class="identifier">n</span></code> 189 shall equal the value passed as the first argument to the invocation 190 of <code class="computeroutput"><span class="identifier">allocate</span></code> 191 which returned <code class="computeroutput"><span class="identifier">p</span></code>. 192 </p></dd> 193<dt><span class="term">Effects</span></dt> 194<dd><p> 195 Deallocates the storage referenced by <code class="computeroutput"><span class="identifier">p</span></code>. 196 </p></dd> 197<dt><span class="term">Remarks</span></dt> 198<dd><p> 199 Uses <code class="computeroutput"><span class="special">::</span><span class="keyword">operator</span> 200 <span class="keyword">delete</span></code>. 201 </p></dd> 202</dl> 203</div></dd> 204</dl> 205</div> 206</div> 207<div class="section"> 208<div class="titlepage"><div><div><h4 class="title"> 209<a name="core.default_allocator.reference.operators"></a><a class="link" href="default_allocator.html#core.default_allocator.reference.operators" title="Operators">Operators</a> 210</h4></div></div></div> 211<div class="variablelist"> 212<p class="title"><b></b></p> 213<dl class="variablelist"> 214<dt><span class="term"><code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">constexpr</span> <span class="keyword">bool</span> 215 <span class="keyword">operator</span><span class="special">==(</span><span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&,</span> <span class="keyword">const</span> 216 <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&)</span> 217 <span class="keyword">noexcept</span><span class="special">;</span></code></span></dt> 218<dd><div class="variablelist"> 219<p class="title"><b></b></p> 220<dl class="variablelist"> 221<dt><span class="term">Returns</span></dt> 222<dd><p> 223 <code class="computeroutput"><span class="keyword">true</span></code>. 224 </p></dd> 225</dl> 226</div></dd> 227<dt><span class="term"><code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">constexpr</span> <span class="keyword">bool</span> 228 <span class="keyword">operator</span><span class="special">!=(</span><span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&,</span> <span class="keyword">const</span> 229 <span class="identifier">default_allocator</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&)</span> 230 <span class="keyword">noexcept</span><span class="special">;</span></code></span></dt> 231<dd><div class="variablelist"> 232<p class="title"><b></b></p> 233<dl class="variablelist"> 234<dt><span class="term">Returns</span></dt> 235<dd><p> 236 <code class="computeroutput"><span class="keyword">false</span></code>. 237 </p></dd> 238</dl> 239</div></dd> 240</dl> 241</div> 242</div> 243</div> 244</div> 245<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 246<td align="left"></td> 247<td align="right"><div class="copyright-footer">Copyright © 2014 Peter Dimov<br>Copyright © 2014 Glen Fernandes<br>Copyright © 2014 Andrey Semashev<p> 248 Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost 249 Software License, Version 1.0</a>. 250 </p> 251</div></td> 252</tr></table> 253<hr> 254<div class="spirit-nav"> 255<a accesskey="p" href="checked_delete.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="demangle.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 256</div> 257</body> 258</html> 259
