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  27 <a name="core.default_allocator"></a><a class="link" href="default_allocator.html" title="default_allocator">default_allocator</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="default_allocator.html#core.default_allocator.overview">Overview</a></span></dt>
  31 <dt><span class="section"><a href="default_allocator.html#core.default_allocator.examples">Examples</a></span></dt>
  32 <dt><span class="section"><a href="default_allocator.html#core.default_allocator.reference">Reference</a></span></dt>
  33 </dl></div>
  34 <div class="simplesect">
  35 <div class="titlepage"><div><div><h3 class="title">
  36 <a name="idm46687077280048"></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 &lt;boost/core/default_allocator.hpp&gt; 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">&lt;</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">&lt;</span><span class="identifier">Key</span><span class="special">&gt;,</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">&lt;</span><span class="identifier">Key</span><span class="special">&gt;</span> <span class="special">&gt;</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">&lt;</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">&gt;</span>
  86 <span class="identifier">enable_if_t</span><span class="special">&lt;!</span><span class="identifier">is_array_v</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;,</span> <span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&gt;</span>
  87 <span class="identifier">make_shared</span><span class="special">(</span><span class="identifier">Args</span><span class="special">&amp;&amp;...</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">default_allocator</span><span class="special">&lt;</span><span class="identifier">remove_cv_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span> <span class="special">&gt;(),</span>
  90         <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">Args</span><span class="special">&gt;(</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">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;</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">&lt;</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&gt;</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">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</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">&lt;</span><span class="identifier">U</span><span class="special">&gt;</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">&lt;</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">&gt;</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">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;)</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">&lt;</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">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;,</span>
 129     <span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;)</span> <span class="keyword">noexcept</span><span class="special">;</span>
 130
 131 <span class="keyword">template</span><span class="special">&lt;</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">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;,</span>
 133     <span class="keyword">const</span> <span class="identifier">default_allocator</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;)</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">&lt;</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">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;,</span> <span class="keyword">const</span>
 216             <span class="identifier">default_allocator</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;)</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">&lt;</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">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;&amp;,</span> <span class="keyword">const</span>
 229             <span class="identifier">default_allocator</span><span class="special">&lt;</span><span class="identifier">U</span><span class="special">&gt;&amp;)</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>
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