While testing a prototype game save
feature for Vulcan, I ran into a nasty little bug. I would move my
king off of it's attack board, the program would start 'thinking',
and then it would crash. The crash was at an assertion indicating
that the program couldn't find my king anywhere on the board.
After much investigation, which among
other things included rerunning the same move a zillion times and
adding an ASCII print of the entire board at a couple of points just
before the crash, the problem became apparent. I found that the
program had 'imagined' that its queen had captured my king as part of
it's 'thinking' process. From there, tracing back through a long
chain of function calls turned up the bug. There seemed to be
nothing to keep the program from considering moves where one of its
pieces would capture the king. Adding an additional condition to an
existing 'if' statement squashed the bug.
I've gotta say, I got lucky in the
timing of finding this bug. It would have taken a lot
longer to 
fix without having already implemented an ability to return
to the game state just before the crash.
fix without having already implemented an ability to return
to the game state just before the crash.
A patch to fix this bug can be
downloaded from
http://sourceforge.net/projects/vulcanchessmods/files/cricital_patches/king_bug/.
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