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  27 <a name="core.first_scalar"></a><a class="link" href="first_scalar.html" title="first_scalar">first_scalar</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="first_scalar.html#core.first_scalar.overview">Overview</a></span></dt>
  31 <dt><span class="section"><a href="first_scalar.html#core.first_scalar.examples">Examples</a></span></dt>
  32 <dt><span class="section"><a href="first_scalar.html#core.first_scalar.reference">Reference</a></span></dt>
  33 <dt><span class="section"><a href="first_scalar.html#core.first_scalar.history">History</a></span></dt>
  34 </dl></div>
  35 <div class="simplesect">
  36 <div class="titlepage"><div><div><h3 class="title">
  37 <a name="idm46687075668688"></a>Authors</h3></div></div></div>
  38 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
  39           Glen Fernandes
  40         </li></ul></div>
  41 </div>
  42 <div class="section">
  43 <div class="titlepage"><div><div><h3 class="title">
  44 <a name="core.first_scalar.overview"></a><a class="link" href="first_scalar.html#core.first_scalar.overview" title="Overview">Overview</a>
  45 </h3></div></div></div>
  46 <p>
  47         The header &lt;boost/core/first_scalar.hpp&gt; provides the function templates
  48         <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">first_scalar</span></code> that can be used to obtain
  49         a pointer to the first scalar element of an array. Given a pointer of type
  50         <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span></code>
  51         they return a pointer of type <code class="computeroutput"><span class="identifier">remove_all_extents_t</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;*</span></code>.
  52         The functions are <code class="computeroutput"><span class="keyword">constexpr</span></code>
  53         and can be used in constant expressions.
  54       </p>
  55 </div>
  56 <div class="section">
  57 <div class="titlepage"><div><div><h3 class="title">
  58 <a name="core.first_scalar.examples"></a><a class="link" href="first_scalar.html#core.first_scalar.examples" title="Examples">Examples</a>
  59 </h3></div></div></div>
  60 <p>
  61         The following function uses an allocator to allocate an array of arrays and
  62         constructs each scalar element in it.
  63       </p>
  64 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">alloc_construct</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  65 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">first_scalar</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  66
  67 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">A</span><span class="special">&gt;</span>
  68 <span class="keyword">auto</span> <span class="identifier">create</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">A</span><span class="special">&amp;</span> <span class="identifier">allocator</span><span class="special">)</span>
  69 <span class="special">{</span>
  70     <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator_traits</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;::</span><span class="keyword">template</span>
  71         <span class="identifier">rebind_alloc</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">[</span><span class="number">2</span><span class="special">][</span><span class="number">3</span><span class="special">]&gt;</span> <span class="identifier">other</span><span class="special">(</span><span class="identifier">allocator</span><span class="special">);</span>
  72     <span class="keyword">auto</span> <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">other</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">4</span><span class="special">);</span>
  73     <span class="keyword">try</span> <span class="special">{</span>
  74         <span class="identifier">boost</span><span class="special">::</span><span class="identifier">alloc_construct_n</span><span class="special">(</span><span class="identifier">other</span><span class="special">,</span>
  75             <span class="identifier">boost</span><span class="special">::</span><span class="identifier">first_scalar</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">to_address</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">)),</span> <span class="number">24</span><span class="special">);</span>
  76     <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(...)</span> <span class="special">{</span>
  77         <span class="identifier">other</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">,</span> <span class="number">4</span><span class="special">);</span>
  78         <span class="keyword">throw</span><span class="special">;</span>
  79     <span class="special">}</span>
  80     <span class="keyword">return</span> <span class="identifier">ptr</span><span class="special">;</span>
  81 <span class="special">}</span>
  82 </pre>
  83 </div>
  84 <div class="section">
  85 <div class="titlepage"><div><div><h3 class="title">
  86 <a name="core.first_scalar.reference"></a><a class="link" href="first_scalar.html#core.first_scalar.reference" title="Reference">Reference</a>
  87 </h3></div></div></div>
  88 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
  89
  90 <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>
  91 <span class="keyword">constexpr</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">first_scalar</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="keyword">noexcept</span><span class="special">;</span>
  92
  93 <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="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">&gt;</span>
  94 <span class="keyword">constexpr</span> <span class="keyword">auto</span> <span class="identifier">first_scalar</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">N</span><span class="special">])</span> <span class="keyword">noexcept</span><span class="special">;</span>
  95
  96 <span class="special">}</span> <span class="comment">/* boost */</span>
  97 </pre>
  98 <div class="section">
  99 <div class="titlepage"><div><div><h4 class="title">
 100 <a name="core.first_scalar.reference.functions"></a><a class="link" href="first_scalar.html#core.first_scalar.reference.functions" title="Functions">Functions</a>
 101 </h4></div></div></div>
 102 <div class="variablelist">
 103 <p class="title"><b></b></p>
 104 <dl class="variablelist">
 105 <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">&gt;</span> <span class="keyword">constexpr</span>
 106             <span class="identifier">T</span><span class="special">*</span>
 107             <span class="identifier">first_scalar</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="keyword">noexcept</span><span class="special">;</span></code></span></dt>
 108 <dd><div class="variablelist">
 109 <p class="title"><b></b></p>
 110 <dl class="variablelist">
 111 <dt><span class="term">Returns</span></dt>
 112 <dd><p>
 113                       <code class="computeroutput"><span class="identifier">p</span></code>.
 114                     </p></dd>
 115 </dl>
 116 </div></dd>
 117 <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="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span>
 118             <span class="identifier">N</span><span class="special">&gt;</span>
 119             <span class="keyword">constexpr</span> <span class="keyword">auto</span>
 120             <span class="identifier">first_scalar</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">N</span><span class="special">])</span> <span class="keyword">noexcept</span><span class="special">;</span></code></span></dt>
 121 <dd><div class="variablelist">
 122 <p class="title"><b></b></p>
 123 <dl class="variablelist">
 124 <dt><span class="term">Returns</span></dt>
 125 <dd><p>
 126                       <code class="computeroutput"><span class="identifier">first_scalar</span><span class="special">(&amp;(*</span><span class="identifier">p</span><span class="special">)[</span><span class="number">0</span><span class="special">])</span></code>.
 127                     </p></dd>
 128 </dl>
 129 </div></dd>
 130 </dl>
 131 </div>
 132 </div>
 133 </div>
 134 <div class="section">
 135 <div class="titlepage"><div><div><h3 class="title">
 136 <a name="core.first_scalar.history"></a><a class="link" href="first_scalar.html#core.first_scalar.history" title="History">History</a>
 137 </h3></div></div></div>
 138 <p>
 139         Glen Fernandes implemented <code class="computeroutput"><span class="identifier">first_scalar</span></code>.
 140         Peter Dimov suggested a change for GCC to support an additional <code class="computeroutput"><span class="keyword">constexpr</span></code> use.
 141       </p>
 142 </div>
 143 </div>
 144 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 145 <td align="left"></td>
 146 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Peter Dimov<br>Copyright &#169; 2014 Glen Fernandes<br>Copyright &#169; 2014 Andrey Semashev<p>
 147         Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost
 148         Software License, Version 1.0</a>.
 149       </p>
 150 </div></td>
 151 </tr></table>
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