[computer-go] C++ pointer question

[Weston Markham]

Whoa!  I believe that this is quite bad advice.  These are low-level
functions, to be called many, many times over the course of a run.
There should not be any dynamic memory allocated or freed in dilate()!
 (Especially not if an automatic variable will accomplish the same
thing.)  I would even guess that there should not be any dynamic
memory allocated or freed in the constructor & destructor, either,
although that may be less of a problem, given that it provides some
flexibility at run time.

Weston

On 8/8/06, Berk Ozbozkurt <ozbozkurt at fisek.com.tr> wrote:
> Peter Drake wrote:
>
> > Okay, I've got this method in my BitBoard class:
> >
> > void dilate() // Expand to include all adjacent points
> > {
> >     BitBoard temp;
> >     temp.bits[0] = bits[0] | (bits[0] << 1) | (bits[0] >> 1) | bits[1];
> >     temp.bits[board_width - 1] = bits[board_width - 1] | (bits
> > [board_width - 1] << 1)
> >         | (bits[board_width - 1] >> 1) | bits[board_width - 2];
> >     for (unsigned row = 1; row < board_width - 1; row++) {
> >         temp.bits[row] = bits[row] | (bits[row] << 1) | (bits[row] >>
> > 1) |  bits[row - 1] | bits[row + 1];
> >     }
> >     for (unsigned row = 0; row < board_width; row++) {
> >         bits[row] = temp.bits[row];
> >     }
> > }
> >
> > Is there some way to avoid that second for loop? I tried "this =
> > temp" and "*this = *temp", but the compiler isn't happy with either.
> >
> It has been quite a while since I used C++, but IIRC (and assuming you
> have not overloaded [, ], << and >> operators) you can store your data
> (bits) in a dynamic array. In that case a simple assignment will work:
>
> class Bitboard{
>     bits_type *bits;
>     Bitboard()
>     {
>             bits=new bits_type[ARRAY_SIZE];
>            ....
>      }
>     ~Bitboard()
>     {
>             delete[] bits;
>            ....
>      }
> void dilate() // Expand to include all adjacent points
> {
>     bits_type *temp=new bits_type[ARRAY_SIZE];
>     temp.bits[0] = bits[0] | (bits[0] << 1) | (bits[0] >> 1) | bits[1];
> ...
>     delete[] bits;
>     bits=temp;
>    }
> }
>
> }
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