Re: [fpc-pascal] Free Pascal bindings for EyeLink C code (with a god-cast)
On 13-6-2023 15:38, Rafael Picanço via fpc-pascal wrote: Thank you Marco, I am elaborating on top of your suggestions. > The problem is that the logical solution, making it a macro, doesn't work, as macro definitions don't export through USES clauses. I think that pre-processor constants with $I would be a valid alternative for using the best solution. For example: A matter of taste. I would have as less macros as possible. Moreover the typed const doesn't require including additional files at the usage site, so IMHO it is objectively a better solution ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Free Pascal bindings for EyeLink C code (with a god-cast)
Thank you Marco, I am elaborating on top of your suggestions.
> The problem is that the logical solution, making it a macro, doesn't
work, as macro definitions don't export through USES clauses.
I think that pre-processor constants with $I would be a valid alternative
for using the best solution. For example:
// constants.pp
{$MACRO ON}
{$ifndef EXTERNAL_DEV_NONE}
{$DEFINE EXTERNAL_DEV_NONE := TGetExButtonStatesFunction(Pointer(0))}
{$endif}
{$ifndef EXTERNAL_DEV_CEDRUS}
{$DEFINE EXTERNAL_DEV_CEDRUS := TGetExButtonStatesFunction(Pointer(1))}
{$endif}
{$ifndef EXTERNAL_DEV_SYS_KEYBOARD}
{$DEFINE EXTERNAL_DEV_SYS_KEYBOARD :=
TGetExButtonStatesFunction(Pointer(2))}
{$endif}
program godcastsucks;
{$I constants}
type
PCCDBS = ^TCCDBS;
TCCDBS = record
userdata: Pointer;
buttons: array[0..255] of AnsiChar;
internal: Pointer;
end;
TGetExButtonStatesFunction = function (accdbs: PCCDBS): Int32; cdecl;
function enable_external_calibration_device(
buttonStatesfcn: Pointer {other arguments removed for simplicity}):
Int32; cdecl;
var
Statesfcn : TGetExButtonStatesFunction;
begin
Result := Int32(TGetExButtonStatesFunction(@buttonStatesfcn^));
case Result of
0 : { do nothing };
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(EXTERNAL_DEV_NONE));
WriteLn(enable_external_calibration_device(@ExButtonStatesFunction));
ReadLn;
end.
> Note that an alternative for this macro exists since FPC 3.2.0:
Thank you for the reference!
On Tue, Jun 13, 2023 at 7:00 AM
wrote:
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>1. Re: Free Pascal bindings for EyeLink C code (with a
> god-cast) (Marco van de Voort)
>
>
> --
>
> Message: 1
> Date: Tue, 13 Jun 2023 11:25:13 +0200
> From: Marco van de Voort
> To: fpc-pascal@lists.freepascal.org
> Subject: Re: [fpc-pascal] Free Pascal bindings for EyeLink C code
> (with a god-cast)
> Message-ID:
> <5a5a8eac-e91d-d9d7-4131-d7301ec3c...@pascalprogramming.org>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
>
> On 13-6-2023 05:19, Rafael Pican?o via fpc-pascal wrote:
> > (1) I have no idea on how to translate these god-casts, eg.,
> > ((getExButtonStates)0), to free pascal. Right now, I think that even
> > if I don't really need them, I just want?to understand and learn
> > in?the?process.
>
> The problem is that the logical solution, making it a macro, doesn't
> work, as macro definitions don't export through USES clauses.
>
> Defining it a proper constant would be the best solution, but FPC
> doesn't like it :
>
> const
>
> ?EXTERNAL_DEV_NONE = TGetExButtonStatesFunction(pointer(0));
>
> so the next best is turning it into a type constant at the expense of
> sizeof(pointer) bytes in the binary:
>
> const
>
> ? EXTERNAL_DEV_NONE : TGetExButtonStatesFunction= pointer(0);
>
> etc etc.
>
> >
> > (2) So, the whole point here is?binding the
> > "enable_external_calibration_device" function. It expects a
> > "getExButtonStates buttonStatesfcn". Can you check if my current
> > binding is right?
> >
> A purist would say it needs to be "ansichar" rather than char (because
> in future unicode modes char could be 2-byte, for the rest it seems ok.
>
> > (3) I am using the?ELCALLTYPE?macro just because?they were?using them
> > too,?I am assuming backward compatibility. But I am not sure if I
> > really need them. EyeLink code depends on custom SDL2 headers and I
> > am?running SDL2 Free Pascal related stuff just fine (and it has cdecl
> > in everything). What do you think about that? For reference, this is
> > the macro:
> >
> You must match the calling convention of the implementation. Some
> functions have target dependent calling conventions, some non native
> libraries force cdecl even on Windows. (where stdcall or fastcall is
> more conventional)
>
> Note that an alternative for this macro exists since FPC 3.2.0:
>
>
> https://wiki.freepascal.org/FPC_New_Features_3.2.0#Support_for_WinAPI_directive
>
> Even though the naming is not "elegant" for crossplatform usage.
>
>
> --
>
> Subject: Digest Footer
>
>
Re: [fpc-pascal] fpc isn't optimised for tail recursion, is it?
Le 12/06/2023 à 19:05, Steve Litt via fpc-pascal a écrit : Busted! I used Pascal 1984-1993 So I guess you are not familiar too with the "Result" variable which appeared with Delphi 1 in 1995 if I remember correctly. nextt:= num; can be written to as : Result:= num; https://www.freepascal.org/docs-html/ref/refse94.html I prefer Result because it reduces risks of confusion with recursive call and you can eventually take the address of Result with @Result (where @nextt would take the address of the function nextt), pass it by reference to another function ( e.g. FillChar( Result, SizeOf(Result), 0); ) , it behaves like a normal variable.___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Free Pascal bindings for EyeLink C code (with a god-cast)
On 13-6-2023 05:19, Rafael Picanço via fpc-pascal wrote: (1) I have no idea on how to translate these god-casts, eg., ((getExButtonStates)0), to free pascal. Right now, I think that even if I don't really need them, I just want to understand and learn in the process. The problem is that the logical solution, making it a macro, doesn't work, as macro definitions don't export through USES clauses. Defining it a proper constant would be the best solution, but FPC doesn't like it : const EXTERNAL_DEV_NONE = TGetExButtonStatesFunction(pointer(0)); so the next best is turning it into a type constant at the expense of sizeof(pointer) bytes in the binary: const EXTERNAL_DEV_NONE : TGetExButtonStatesFunction= pointer(0); etc etc. (2) So, the whole point here is binding the "enable_external_calibration_device" function. It expects a "getExButtonStates buttonStatesfcn". Can you check if my current binding is right? A purist would say it needs to be "ansichar" rather than char (because in future unicode modes char could be 2-byte, for the rest it seems ok. (3) I am using the ELCALLTYPE macro just because they were using them too, I am assuming backward compatibility. But I am not sure if I really need them. EyeLink code depends on custom SDL2 headers and I am running SDL2 Free Pascal related stuff just fine (and it has cdecl in everything). What do you think about that? For reference, this is the macro: You must match the calling convention of the implementation. Some functions have target dependent calling conventions, some non native libraries force cdecl even on Windows. (where stdcall or fastcall is more conventional) Note that an alternative for this macro exists since FPC 3.2.0: https://wiki.freepascal.org/FPC_New_Features_3.2.0#Support_for_WinAPI_directive Even though the naming is not "elegant" for crossplatform usage. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
[fpc-pascal] Free Pascal bindings for EyeLink C code (with a god-cast)
Hi everyone,
First of all, I am sorry if this is not the best place for this
interoperability issue.
The problem I want to solve is how to make a Free Pascal binding for to the
following piece of C code:
typedef struct _CCDBS {
void *userdata;
char buttons[256];
void *internal;
}CCDBS;
typedef int (ELCALLBACK *getExButtonStates)(CCDBS *);
#define EXTERNAL_DEV_NONE ((getExButtonStates)0)
#define EXTERNAL_DEV_CEDRUS ((getExButtonStates)1)
#define EXTERNAL_DEV_SYS_KEYBOARD ((getExButtonStates)2)
int ELCALLTYPE enable_external_calibration_device(getExButtonStates
buttonStatesfcn, const char * config, void *userData);
Questions
(1) I have no idea on how to translate these god-casts, eg.,
((getExButtonStates)0), to free pascal. Right now, I think that even if I
don't really need them, I just want to understand and learn in the process.
(2) So, the whole point here is binding the
"enable_external_calibration_device" function. It expects a
"getExButtonStates buttonStatesfcn". Can you check if my current binding is
right?
type
PCCDBS = ^TCCDBS;
TCCDBS = record
userdata: Pointer;
buttons: array[0..255] of Char;
internal: Pointer;
end;
TGetExButtonStatesFunction = function (accdbs: PCCDBS): Int32; ELCALLTYPE
function enable_external_calibration_device(
buttonStatesfcn: TGetExButtonStatesFunction;
config: PChar; userData: Pointer): Int32; ELCALLTYPE ELDLL
(3) I am using the ELCALLTYPE macro just because they were using them
too, I am assuming backward compatibility. But I am not sure if I really
need them. EyeLink code depends on custom SDL2 headers and I am running
SDL2 Free Pascal related stuff just fine (and it has cdecl in everything).
What do you think about that? For reference, this is the macro:
{$ifndef ELCALLTYPE}
{$IFDEF Windows}
{$DEFINE ELCALLTYPE := stdcall;}
{$ELSEIF Linux}
{$DEFINE ELCALLTYPE := cdecl;}
{$ELSE}
{$DEFINE ELCALLTYPE := cdecl;}
{$ENDIF}
{$endif}
(4) I can send the code and soon will release it on my GitHub (cpicanco).
Best.
R
PS.: You can find a related discussion here
https://stackoverflow.com/questions/76427311/free-pascal-bindings-for-a-typedef-function-inside-a-define-macro-and-a-number-o
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