Hi Tomas,
On top of your suggestion, the only way to make FPC happy is to assign nil
to the type constants and then assign the corresponding pointers to them
somewhere:
unit eyelink.constants
interface
const
EXTERNAL_DEV_NONE : TGetExButtonStatesFunction = nil;
EXTERNAL_DEV_CEDRUS : TGetExButtonStatesFunction = nil;
EXTERNAL_DEV_SYS_KEYBOARD : TGetExButtonStatesFunction = nil;
implementation
initialization
EXTERNAL_DEV_NONE := TGetExButtonStatesFunction(Pointer(0));
EXTERNAL_DEV_CEDRUS := TGetExButtonStatesFunction(Pointer(1));
EXTERNAL_DEV_SYS_KEYBOARD := TGetExButtonStatesFunction(Pointer(2));
end.
program godcastsucks;
uses eyelink.constants;
function enable_external_calibration_device(
buttonStatesfcn: TGetExButtonStatesFunction
{other arguments removed for simplicity}): Int32; cdecl;
var
Statesfcn : TGetExButtonStatesFunction;
begin
if buttonStatesfcn = nil then
begin
WriteLn('Function is nil');
end else begin
WriteLn('Function is not nil');
end;
Result := Int32(buttonStatesfcn);
case Result of
0 : { do something };
1 : { do something };
2 : { do something }
else
begin
Statesfcn := TGetExButtonStatesFunction(buttonStatesfcn);
Statesfcn(nil);
Result := -1;
end;
end;
end;
function ExButtonStatesFunction(accdbs: PCCDBS): Int32; cdecl;
begin
WriteLn('God casts sucks');
end;
begin
WriteLn(enable_external_calibration_device(TGetExButtonStatesFunction(EXTERNAL_DEV_CEDRUS)));
WriteLn(enable_external_calibration_device(@ExButtonStatesFunction));
ReadLn;
end.
Best,
R
PS. If you find a better solution, please make me known!
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