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    <p>If you want to fill 100 (or even 1000) <code>unsigned int</code> elements, then you can choose any method you want, be it <code>std::fill_n</code>, or <code>for</code> loop - the number is so small you won't see the difference, even if you do this operation very often.</p> <p>However, if you want to set values for a bigger array, say, 8k x 8k texture with pixels composed of 4 unsigned color components, then there is a short comparison of the methods you can use:</p> <pre><code>#include &lt;iostream&gt; #include &lt;ctime&gt; #include &lt;cstdint&gt; int main(){ long unsigned const size = 8192 * 8192 * 4; unsigned* arr = new unsigned[size]; clock_t t1 = clock(); memset(arr, 0, size*sizeof(unsigned)); clock_t t2 = clock(); std::fill_n(arr, size, 123); clock_t t3 = clock(); for(int i = 0; i &lt; size; ++i) *(arr + i) = 123; clock_t t4 = clock(); int64_t val = 123; val = val &lt;&lt; 32 | 132; for(int i = 0; i &lt; size / 2; ++i) *(int64_t*)(arr + i * 2) = val; clock_t t5 = clock(); std::cout &lt;&lt; "memset = " &lt;&lt; t2 - t1 &lt;&lt; std::endl; std::cout &lt;&lt; "std::fill_n = " &lt;&lt; t3 - t2 &lt;&lt; std::endl; std::cout &lt;&lt; "for 32 = " &lt;&lt; t4 - t3 &lt;&lt; std::endl; std::cout &lt;&lt; "for 64 = " &lt;&lt; t5 - t4 &lt;&lt; std::endl; delete arr; return 0; } </code></pre> <p><strong>1. <code>memset</code></strong></p> <p>This function is used here only to show you how fast <em>zeroing</em> your array could be, in comparison to other methods. It's the fastest solution, but only usable when you want to set every byte to the same value (especially useful with <code>0</code> and <code>0xFF</code> in your case, I guess).</p> <p><strong>2. <code>std::fill_n</code> and <code>for</code> loop with 32-bit value</strong></p> <p><code>std::fill_n</code> looks to be the slowest of the solutions, and it is even slightly <strong>slower</strong> than the <code>for</code> solution with 32-bit values.</p> <p><strong>3. <code>for</code> loop with 64-bit value ON 64-bit SYSTEM</strong></p> <p>I guess this is the solution you could go for, since it wins this competition. However, if your machine were 32-bit, then I would expect the results to be comparable to the loop with 32-bit values (depends on the compiler and processor), since processor will handle one 64-bit value as two 32-bit values.</p>
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