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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_typetraits.examples.fill"></a><a class="link" href="fill.html" title="An Optimised Version of std::fill">An Optimised Version
  28       of std::fill</a>
  29 </h3></div></div></div>
  30 <p>
  31         Demonstrates a version of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">fill</span></code>
  32         that uses <code class="computeroutput"><a class="link" href="../reference/has_trivial_assign.html" title="has_trivial_assign">has_trivial_assign</a></code>
  33         to determine whether to use <code class="computeroutput"><span class="identifier">memset</span></code>
  34         to optimise the fill operation (see <a href="../../../../examples/fill_example.cpp" target="_top">fill_example.cpp</a>):
  35       </p>
  36 <pre class="programlisting"><span class="comment">//</span>
  37 <span class="comment">// fill</span>
  38 <span class="comment">// same as std::fill, but uses memset where appropriate</span>
  39 <span class="comment">//</span>
  40 <span class="keyword">namespace</span> <span class="identifier">detail</span><span class="special">{</span>
  41
  42 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">I</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">b</span><span class="special">&gt;</span>
  43 <span class="keyword">void</span> <span class="identifier">do_fill</span><span class="special">(</span><span class="identifier">I</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">I</span> <span class="identifier">last</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">val</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/integral_constant.html" title="integral_constant">integral_constant</a><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">b</span><span class="special">&gt;&amp;)</span>
  44 <span class="special">{</span>
  45    <span class="keyword">while</span><span class="special">(</span><span class="identifier">first</span> <span class="special">!=</span> <span class="identifier">last</span><span class="special">)</span>
  46    <span class="special">{</span>
  47       <span class="special">*</span><span class="identifier">first</span> <span class="special">=</span> <span class="identifier">val</span><span class="special">;</span>
  48       <span class="special">++</span><span class="identifier">first</span><span class="special">;</span>
  49    <span class="special">}</span>
  50 <span class="special">}</span>
  51
  52 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
  53 <span class="keyword">void</span> <span class="identifier">do_fill</span><span class="special">(</span><span class="identifier">T</span><span class="special">*</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">last</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">val</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/integral_constant.html" title="integral_constant">true_type</a><span class="special">&amp;)</span>
  54 <span class="special">{</span>
  55    <span class="identifier">std</span><span class="special">::</span><span class="identifier">memset</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">val</span><span class="special">,</span> <span class="identifier">last</span><span class="special">-</span><span class="identifier">first</span><span class="special">);</span>
  56 <span class="special">}</span>
  57
  58 <span class="special">}</span>
  59
  60 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">I</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  61 <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">fill</span><span class="special">(</span><span class="identifier">I</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">I</span> <span class="identifier">last</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">val</span><span class="special">)</span>
  62 <span class="special">{</span>
  63    <span class="comment">//</span>
  64    <span class="comment">// We can do an optimised fill if T has a trivial assignment </span>
  65    <span class="comment">// operator and if it's size is one:</span>
  66    <span class="comment">//</span>
  67    <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/integral_constant.html" title="integral_constant">integral_constant</a><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">,</span>
  68       <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/has_trivial_assign.html" title="has_trivial_assign">has_trivial_assign</a><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&amp;&amp;</span> <span class="special">(</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span> <span class="special">==</span> <span class="number">1</span><span class="special">)&gt;</span> <span class="identifier">truth_type</span><span class="special">;</span>
  69    <span class="identifier">detail</span><span class="special">::</span><span class="identifier">do_fill</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">val</span><span class="special">,</span> <span class="identifier">truth_type</span><span class="special">());</span>
  70 <span class="special">}</span>
  71 </pre>
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