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    <p>Even though the two function arguments can be <em>consumed</em> in the same way, namely via <code>m[i][j]</code>, they're quite different:</p> <ul> <li><p><code>int m[M][N]</code> is an array of <code>M</code> arrays of <code>N</code> ints.</p></li> <li><p><code>int **m</code> is a pointer to a pointer to an int.</p></li> </ul> <p>You cannot pass arrays as function arguments, so an "array of <code>K</code> elements of type <code>T</code>" decays to a "poin&shy;ter-to-<code>T</code>", pointing to the first element of the array. Thus it is permissible and equivalent to write the first form as <code>int m[][N]</code> in a function argument, since the value <code>M</code> is lost. However, the value <code>N</code> is <em>not</em> lost; it is part of the type!</p> <p>So the following are admissible/erroneous for the first form:</p> <pre><code>void f(int arr[M][N]); int a[M][N]; int b[2*M][N]; int c[M][N + 1]; f(a); // OK f(b); // OK; slowest extent is forgotten in the decay //f(c); // Error! 'c' is not an array of {array of N ints}. </code></pre> <p>For the second form, the meaning is rather different:</p> <pre><code>void g(int **p); int a; int * pa = &amp;a; g(&amp;pa); // fine, pointer to 'pa' int arr[M][N]; // g(arr); // Error, makes no sense </code></pre> <p>The expression <code>arr</code> designates the pointer to the first element of an array of arrays of <code>N</code> integers, i.e. its type is <code>int (*)[N]</code>. Dereferencing it gives an array of <code>N</code> integers, and <em>not</em> a pointer to an integer.</p> <p>There is no way to convert the expression <code>arr</code> into a pointer to a pointer: If you said,</p> <pre><code>int ** fool = (int**)arr; </code></pre> <p>then <code>*fool</code> would point to the first element of the first array (<code>arr[0]</code>), and <em>not to an <code>int</code> pointer</em>. So you cannot dereference the value further, because the value <em>is not a pointer</em>.</p> <p>The only <em>correct</em> way to pass a two-dimensional array as a double pointer is to construct an intermediate helper array:</p> <pre><code>int * helper[M]; // array of pointers for (size_t i = 0; i != M; ++i) { helper[i] = arr[i]; // implicit decay } g(helper); // or "g(&amp;helper[0])" </code></pre>
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    1. POWhat is the difference between array[ROWS][COLS] and **array
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    1. COthis is a really well explained answer, thank you
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