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POWhich one is more optimized for accessing array?
 

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  1. POWhich one is more optimized for accessing array?
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    <p>Solving the following exercise:</p> <blockquote> <p>Write three different versions of a program to print the elements of ia. One version should use a range for to manage the iteration, the other two should use an ordinary for loop in one case using subscripts and in the other using pointers. In all three programs write all the types directly. That is, do not use a type alias, auto, or decltype to simplify the code.[C++ Primer]</p> </blockquote> <p>a question came up: <strong>Which of these methods for accessing array is optimized in terms of speed and why?</strong> </p> <hr> <p><strong>My Solutions:</strong></p> <ol> <li><p>Foreach Loop:</p> <pre><code>int ia[3][4]={{1,2,3,4},{5,6,7,8},{9,10,11,12}}; for (int (&amp;i)[4]:ia) //1st method using for each loop for(int j:i) cout&lt;&lt;j&lt;&lt;" "; </code></pre></li> <li><p>Nested for loops:</p> <pre><code>for (int i=0;i&lt;3;i++) //2nd method normal for loop for(int j=0;j&lt;4;j++) cout&lt;&lt;ia[i][j]&lt;&lt;" "; </code></pre></li> <li><p>Using pointers:</p> <pre><code>int (*i)[4]=ia; for(int t=0;t&lt;3;i++,t++){ //3rd method. using pointers. for(int x=0;x&lt;4;x++) cout&lt;&lt;(*i)[x]&lt;&lt;" "; </code></pre></li> <li><p>Using <code>auto</code>:</p> <pre><code>for(auto &amp;i:ia) //4th one using auto but I think it is similar to 1st. for(auto j:i) cout&lt;&lt;j&lt;&lt;" "; </code></pre></li> </ol> <hr> <p><strong>Benchmark result using <code>clock()</code></strong></p> <pre class="lang-none prettyprint-override"><code>1st: 3.6 (6,4,4,3,2,3) 2nd: 3.3 (6,3,4,2,3,2) 3rd: 3.1 (4,2,4,2,3,4) 4th: 3.6 (4,2,4,5,3,4) </code></pre> <p>Simulating each method 1000 times: </p> <pre class="lang-none prettyprint-override"><code>1st: 2.29375 2nd: 2.17592 3rd: 2.14383 4th: 2.33333 Process returned 0 (0x0) execution time : 13.568 s </code></pre> <p>Compiler used:MingW 3.2 c++11 flag enabled. IDE:CodeBlocks</p>
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    1. COAFAIK c compilers are good enough at optimizing "normal for loop", so I'd prefer it (for readability)
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      1. USAnton Kovalenko
    2. CO@AntonKovalenko i used it mostly but don't know is their any advantage of others over this one.
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    3. COReadability, readability, readability ...
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