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copied!<p>2D C-style arrays in C and C++ are a block of memory of size <code>rows * columns * sizeof(datatype)</code> bytes.</p> <p>The actual [row][column] dimensions exist only statically at compile time. There's nothing there dynamically at runtime!</p> <p>So, as others have mentioned, you can implement</p> <pre><code> int array [ rows ] [ columns ]; </code></pre> <p>As:</p> <pre><code> int array [ rows * columns ] </code></pre> <p>Or as:</p> <pre><code> int * array = malloc ( rows * columns * sizeof(int) ); </code></pre> <hr> <p>Next: Declaring a variably sized array. <strong>In C</strong> this is possible:</p> <pre><code>int main( int argc, char ** argv ) { assert( argc > 2 ); int rows = atoi( argv[1] ); int columns = atoi( argv[2] ); assert(rows > 0 && columns > 0); int data [ rows ] [ columns ]; // Yes, legal! memset( &data, 0, sizeof(data) ); print( rows, columns, data ); manipulate( rows, columns, data ); print( rows, columns, data ); } </code></pre> <hr> <p><strong>In C</strong> you can just pass the variably-sized array around the same as a non-variably-sized array:</p> <pre><code>void manipulate( int theRows, int theColumns, int theData[theRows][theColumns] ) { for ( int r = 0; r < theRows; r ++ ) for ( int c = 0; c < theColumns; c ++ ) theData[r][c] = r*10 + c; } </code></pre> <p><strong>However, in C++</strong> that is not possible. You need to allocate the array using dynamic allocation, e.g.: </p> <pre><code>int *array = new int[rows * cols](); </code></pre> <p>or preferably (with automated memory management)</p> <pre><code>std::vector<int> array(rows * cols); </code></pre> <p>Then the functions must be modified to accept 1-dimensional data:</p> <pre><code>void manipulate( int theRows, int theColumns, int *theData ) { for ( int r = 0; r < theRows; r ++ ) for ( int c = 0; c < theColumns; c ++ ) theData[r * theColumns + c] = r*10 + c; } </code></pre>

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