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    <p>All compilers I know will replace a simple <code>std::copy</code> with a <code>memcpy</code> when it is appropriate, or even better, vectorize the copy so that it would be even faster than a <code>memcpy</code>.</p> <p>In any case: profile and find out yourself. Different compilers will do different things, and it's quite possible it won't do exactly what you ask.</p> <p>See <a href="http://www.linux-kongress.org/2009/slides/compiler_survey_felix_von_leitner.pdf" rel="noreferrer">this presentation on compiler optimisations</a> (pdf).</p> <p>Here's <a href="http://gcc.godbolt.org/#%7B%22version%22%3A3%2C%22filterAsm%22%3A%7B%22labels%22%3Atrue%2C%22directives%22%3Atrue%2C%22commentOnly%22%3Atrue%7D%2C%22compilers%22%3A%5B%7B%22source%22%3A%22%23include%20%3Calgorithm%3E%5Cn%5Cnstruct%20foo%5Cn%7B%5Cn%20%20int%20x%2C%20y%3B%20%20%20%20%5Cn%7D%3B%5Cn%5Cnvoid%20bar(foo*%20a%2C%20foo*%20b%2C%20size_t%20n)%5Cn%7B%5Cn%20%20std%3A%3Acopy(a%2C%20a%20%2B%20n%2C%20b)%3B%5Cn%7D%5Cn%22%2C%22compiler%22%3A%22%2Fusr%2Fbin%2Fg%2B%2B-4.7%22%2C%22options%22%3A%22-O%20-march%3Dnative%22%7D%5D%7D" rel="noreferrer">what GCC does</a> for a simple <code>std::copy</code> of a POD type.</p> <pre><code>#include &lt;algorithm&gt; struct foo { int x, y; }; void bar(foo* a, foo* b, size_t n) { std::copy(a, a + n, b); } </code></pre> <p>Here's the disassembly (with only <code>-O</code> optimisation), showing the call to <code>memmove</code>:</p> <pre><code>bar(foo*, foo*, unsigned long): salq $3, %rdx sarq $3, %rdx testq %rdx, %rdx je .L5 subq $8, %rsp movq %rsi, %rax salq $3, %rdx movq %rdi, %rsi movq %rax, %rdi call memmove addq $8, %rsp .L5: rep ret </code></pre> <p>If you change the function signature to</p> <pre><code>void bar(foo* __restrict a, foo* __restrict b, size_t n) </code></pre> <p>then the <code>memmove</code> becomes a <code>memcpy</code> for a slight performance improvement. Note that <code>memcpy</code> itself will be heavily vectorised.</p>
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    1. POIs it better to use std::memcpy() or std::copy() in terms to performance?
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    1. USPeter Alexander
    1. USPeter Alexander
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      1. VTUpMod
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    1. COHow can I do profiling. What tool to use (in windows and linux)?
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      1. USuser576670
    2. COYou don't even need to use a tool for this. Just get the time before the copy, the time after, and subtract to get the time it took :-)
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      1. USPeter Alexander
    3. COIIRC `copy` actually dispatches to `memmove`, not `memcpy` (in the cases where it does that at all) but I think it’s safe to surmise that it does that because it’s even faster.
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      1. USKonrad Rudolph
 

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