[solved] stack overflow error

[speter]

I am getting an exception with the message "External: STACK OVERFLOW" in file uCommon.pas at line 238. begin"

When I click on OK, line 238 is indeed the "begin" of an initialisation procedure; which contains a number of calls to default(), which initialise various arrays in the program.

Recently, I've been reworking how I calculate the distance from a point to other positions on a game board / map.

Interestingly, the exception is occuring at the beginning of the procedure, not at one of the default() calls.

Code: Pascal  [Select][+][-]

1. procedure GameInitialisation;
2. var
3.   a : integer;
4. begin
5.   debugform.AddMessage('begin GameInitialisation');
6.   GameBoard := default(TGameBoard);
7.   debugform.AddMessage(' a');
8.   CityList := default(TCityList);
9.   debugform.AddMessage(' b');
10.   ...

The program is not displaying the "begin ..." message.

Any help / suggestions would be very welcome. I am thinking that the distance data is making the GameBoard variable too large...?

cheers
S.

[ASerge]

Code: Pascal  [Select][+][-]

1. procedure GameInitialisation;
2. var
3.   a : integer;
4. begin
5.   debugform.AddMessage('begin GameInitialisation');
6.   GameBoard := default(TGameBoard);...

When using Default(), FPC uses a temporary variable, which it initializes and assigns. Apparently the type of TGameBoard is very large.
FillChar(GameBoard, SizeOf(GameBoard), 0) may be suitable;

[Thaddy]

Or gameboard is somehow on the stack (procedure local?) and a record type, not a pointer to record. If gameboard is a class that should not happen, because that is always a pointer type and allocated on the heap.
If it is a record (or old school object), a possible solution is to make gameboard a global variable, so it is on the heap or possibly locally use a pointer to gameboard and use New()/Dispose() to allocate on the heap and use pointer dereferences. Third option: increase the stack size with minstacksize and use the formula minstacksize := SizeOf(Gameboard) + Old Stack Size.

[speter]

When using Default(), FPC uses a temporary variable, which it initializes and assigns. Apparently the type of TGameBoard is very large.
FillChar(GameBoard, SizeOf(GameBoard), 0) may be suitable;

Or gameboard is somehow on the stack (procedure local?) and a record type, not a pointer to record. If gameboard is a class that should not happen, because that is always a pointer type and allocated on the heap.
If it is a record, a possible solution is to make gameboard a global variable, so it is on the heap or possibly locally use a pointer to gameboard and use New()/Dispose() to allocate on the heap.

My thanks to you both.

Yes, the gameboard is an array of records. It is declared in a unit called udeclaractions.pas () - which (I thought) would make it a global.

I think, I'll remove the pathing data from the gameboard and have it as a separate (array of records), possibly even as a 2d array of pointers (to the pathing info for the map).

cheers
S.

PS: ASerge's fillchar() suggestion removed the exception!

[Thaddy]

Yes, if you declared it in a unit, depending how, it is global so my remarks do not apply.

[speter]

Yes, if you declared it in a unit, depending how, it is global so my remarks do not apply.

Mp worries. Thanks anyway.

cheers
S.
PS: My current thought (which I'll test today) is to replace the data with a function (since the game "geography" can change through the game).

[jamie]

Yes, if you declared it in a unit, depending how, it is global so my remarks do not apply.

Mp worries. Thanks anyway.

cheers
S.
PS: My current thought (which I'll test today) is to replace the data with a function (since the game "geography" can change through the game).

 If you put at the top of the source where your records are defined, this {$ModeSwitch AdvancedRecords} and insert in your records this.

Code: Pascal  [Select][+][-]

1. TMyRecordTypeName = Record
2. .......
3. Class operator initialize(Var O:TMyRecordTypeName);
4. End;
5. ----
6.  
7. Implementation
8.  
9. class operator initialize(var O:TMyRecordTypeName)
10. Begin
11.  FillByte(O,SizeOF(O),0);
12.  +++ any other inits you need here
13. End;
14.  
15.  

That should have the compiler generate that code in the background, so you don't use Default.

Jamie;

[GannonRidge]

All good now?

[speter]

All good now?

Yes!
As I hinted in my earlier post, I implemented the paths as 2 procedures, 1) CalcPaths(x,y) and 2) GetDirection(p1,p2). Where #1 calc's the paths around a given position and #2 calc's the where to move to head from p1 towards p2.

Despite the above, Jamie's operator initialize() could be very useful where I have Objects (at present I generally include an init() procedure).

cheers
S.

[GannonRidge]

I am glad to hear that