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POTwo-Dimensional Array using Templates
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  1. POTwo-Dimensional Array using Templates
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    copied!<p>I am trying to implement a dynamic array:</p> <pre><code>template &lt;typename Item&gt; class Array { private: Item *_array; int _size; public: Array(); Array(int size); Item&amp; operator[](int index); }; template &lt;typename Item&gt; Array&lt;Item&gt;::Array() { Array(5); } template &lt;typename Item&gt; Array&lt;Item&gt;::Array(int size) { _size = size; _array = new Item [size]; for (int i = 0; i &lt; size; i++) cout &lt;&lt; i &lt;&lt; " " &lt;&lt; _array[i] &lt;&lt; " " &lt;&lt; &amp;_array[i] &lt;&lt; endl; } template &lt;class Item&gt; Item&amp; Array&lt;Item&gt;::operator[](int index) { if (index &lt; 0 || index &gt; _size-1) cout &lt;&lt; "this: " &lt;&lt; this &lt;&lt; ". Index out of range" &lt;&lt; endl; return _array[index]; } </code></pre> <p>When used like this, it works as expected, i.e. prints <code>5</code>:</p> <pre><code>Array&lt; int &gt; testArray(5); testArray[0] = 5; cout &lt;&lt; testArray[0] &lt;&lt; endl; </code></pre> <p>However, I would like to use the class for a two-dimensional dynamic array. I thought that the following would just magically work and print 5...</p> <pre><code>Array&lt; Array&lt;int&gt; &gt; testArray(5); testArray[0][0] = 5; cout &lt;&lt; testArray[0][0] &lt;&lt; endl; </code></pre> <p>...but it does not work. It crashes when I try to set the value at [0][0]. The debugger shows me that <code>this</code> has <code>_size</code> set to 0 and <code>_array</code> to <code>NULL</code>. <code>this</code> at that point points to the first element of the <code>_array</code> of the last created Array instance. </p> <p>One of the things I don't get is when the "inner" array calls its constructor. Stepping through the code, I see that <code>Array(int size)</code> is called once and <code>Array()</code> five times. I would like to create the inner array with a specific size, but using <code>Array&lt; Array&lt;int&gt;(10) &gt; testArray(5)</code> does not compile.</p> <p>Could you provide me with some insight on this? It seems I could not quite wrap my head around templates yet...</p>
 

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