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25 | <div class="section"> | |
26 | <div class="titlepage"><div><div><h3 class="title"> | |
27 | <a name="boost_typetraits.examples.copy"></a><a class="link" href="copy.html" title="An Optimized Version of std::copy">An Optimized Version | |
28 | of std::copy</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">copy</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">memcpy</span></code> | |
34 | to optimise the copy operation (see <a href="../../../../examples/copy_example.cpp" target="_top">copy_example.cpp</a>): | |
35 | </p> | |
36 | <pre class="programlisting"><span class="comment">//</span> | |
37 | <span class="comment">// opt::copy</span> | |
38 | <span class="comment">// same semantics as std::copy</span> | |
39 | <span class="comment">// calls memcpy where appropriate.</span> | |
40 | <span class="comment">//</span> | |
41 | ||
42 | <span class="keyword">namespace</span> <span class="identifier">detail</span><span class="special">{</span> | |
43 | ||
44 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">I1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">I2</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">b</span><span class="special">></span> | |
45 | <span class="identifier">I2</span> <span class="identifier">copy_imp</span><span class="special">(</span><span class="identifier">I1</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">I1</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">I2</span> <span class="identifier">out</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"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">b</span><span class="special">>&)</span> | |
46 | <span class="special">{</span> | |
47 | <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> | |
48 | <span class="special">{</span> | |
49 | <span class="special">*</span><span class="identifier">out</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">first</span><span class="special">;</span> | |
50 | <span class="special">++</span><span class="identifier">out</span><span class="special">;</span> | |
51 | <span class="special">++</span><span class="identifier">first</span><span class="special">;</span> | |
52 | <span class="special">}</span> | |
53 | <span class="keyword">return</span> <span class="identifier">out</span><span class="special">;</span> | |
54 | <span class="special">}</span> | |
55 | ||
56 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> | |
57 | <span class="identifier">T</span><span class="special">*</span> <span class="identifier">copy_imp</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">first</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">out</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">&)</span> | |
58 | <span class="special">{</span> | |
59 | <span class="identifier">memmove</span><span class="special">(</span><span class="identifier">out</span><span class="special">,</span> <span class="identifier">first</span><span class="special">,</span> <span class="special">(</span><span class="identifier">last</span><span class="special">-</span><span class="identifier">first</span><span class="special">)*</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">T</span><span class="special">));</span> | |
60 | <span class="keyword">return</span> <span class="identifier">out</span><span class="special">+(</span><span class="identifier">last</span><span class="special">-</span><span class="identifier">first</span><span class="special">);</span> | |
61 | <span class="special">}</span> | |
62 | ||
63 | ||
64 | <span class="special">}</span> | |
65 | ||
66 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">I1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">I2</span><span class="special">></span> | |
67 | <span class="keyword">inline</span> <span class="identifier">I2</span> <span class="identifier">copy</span><span class="special">(</span><span class="identifier">I1</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">I1</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">I2</span> <span class="identifier">out</span><span class="special">)</span> | |
68 | <span class="special">{</span> | |
69 | <span class="comment">//</span> | |
70 | <span class="comment">// We can copy with memcpy if T has a trivial assignment operator,</span> | |
71 | <span class="comment">// and if the iterator arguments are actually pointers (this last</span> | |
72 | <span class="comment">// requirement we detect with overload resolution):</span> | |
73 | <span class="comment">//</span> | |
74 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special"><</span><span class="identifier">I1</span><span class="special">>::</span><span class="identifier">value_type</span> <span class="identifier">value_type</span><span class="special">;</span> | |
75 | <span class="keyword">return</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">copy_imp</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">out</span><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"><</span><span class="identifier">value_type</span><span class="special">>());</span> | |
76 | <span class="special">}</span> | |
77 | </pre> | |
78 | </div> | |
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83 | Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten | |
84 | Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven | |
85 | Watanabe<p> | |
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