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POIs it better to return values or to write them directly on a given output argument?
 

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  1. POIs it better to return values or to write them directly on a given output argument?
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    <p>I was reading this <a href="https://github.com/bitly/dablooms/pull/19" rel="nofollow" title="Some performance tweaks">pull request on dablooms</a></p> <blockquote> <p>To top it off, Murmur doesn't return the hash value on the stack/registers but writes it directly to a provided buffer. This makes it exceedingly easy to fill the bloom->hashes buffer with a lot of random data and perform the modularization incrementally.</p> </blockquote> <pre><code>for (i = 0; i &lt; bloom-&gt;nsalts; i++, hashes += 4) { MurmurHash3_x64_128(key, key_len, bloom-&gt;salts[i], hashes); hashes[0] = hashes[0] % bloom-&gt;counts_per_func; hashes[1] = hashes[1] % bloom-&gt;counts_per_func; hashes[2] = hashes[2] % bloom-&gt;counts_per_func; hashes[3] = hashes[3] % bloom-&gt;counts_per_func; } </code></pre> <p>I recently noticed that some libraries (at least in C++, my knowledge is pretty limited as I'm quite a newbie) seem not to return values but to instead expect an output argument on which they will write the result. I'm more used to see thing like this:</p> <pre><code>Matrix leftOperand = { /* some values */ }; Matrix rightOperand = { /* some values */ }; Matrix result; result = multiplyMatrices( leftOperand, rightOperand ); </code></pre> <p>Where <code>result</code> is the <code>return</code> value of <code>multiplyMatrices</code>. But learning to use OpenGL, GLEW and freeglut in my most recent project, I see more often than not calls like this:</p> <pre><code>Matrix leftOperand = { /* some values */ }; Matrix rightOperand = { /* some values */ }; Matrix result; multiplyMatrices( leftOperand, rightOperand, result ); </code></pre> <p>I understand what it does, but I find the notation to be odd. However I see that more and more often, and when I saw it 'praised' by the author of above's pull request, I thought there might be a good reason to do that.</p> <p>So in my quest to write less bad and smelly code, I'd like to know if this is good practice. I assume it must be for performance reasons, but I don't see clearly if pushing/poping from the stack is slower than writing directly to a given memory address.</p> <p>I'm looking for some guidelines on the reasons to use one way over another.</p>
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    1. USAntoineG
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    1. COWhich language(s) are you specifically interested in?
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      1. USDan Puzey
    2. CO@DanPuzey the first example is in C, but my use-case would be in C++ and Java.
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