conversion of 2D array to pointer-to-pointer

Activity solution[a][b];

...

Activity **mother = solution;

I want to convert 2D array of objects to pointer-to-pointer. How can I do this;

I searched it on google. however I found only one dimension array example.

A mere conversion won't help you here. There's no compatibility of any kind between 2D array type and pointer-to-pointer type. Such conversion would make no sense.

If you really really need to do that, you have to introduce an extra intermediate "row index" array, which will bridge the gap between 2D array semantics and pointer-to-pointer semantics

Activity solution[a][b];

Activity *solution_rows[a] = { solution[0], solution[1] /* and so on */ };

Activity **mother = solution_rows;

Now accessing mother[i][j] will give you access to solution[i][j].

The reason you can do this for one-dimensional arrays and not two-dimensional arrays has to do with the way in which the actual array elements are stored in memory. For one-dimensional arrays, all of the elements are stored consecutively, so the expression array[i] is equivalent to the expression *(array + i). As you can see, the array size is not needed to perform an array index operation. However, for two-dimensional arrays, the elements are stored in "row major" order, meaning that all of the elements in the zeroth row are stored first, followed by the elements in the first row, followed by the elements in the second row, etc. Therefore, the expression array[i][j] is equivalent to *(array + (i * ROW_SIZE) + j), where ROW_SIZE is the number of elements in each row. Therefore, the array's row size is needed to perform an array index operation, and casting the array variable to a pointer loses that information.