Re: [fpc-pascal] how to use procedure of object in C

2015-03-10 Thread OBones 

Xiangrong Fang wrote:
However, like in my first mail, if I define THandler a procedure of 
object, it makes easier to SetHandler(AMethod); but how can I use that 
procedure of object pointer in the so?


It works the same, cast the data you receive to a TMethod and call the 
code member with the appropriate parameters. So, in the C library do 
this:


typedef struct
{
  Data: Pointer;
  Code: Pointer;
}TMethod;

void SetHandler(TMethod h);
{
  StoredH = h;
}

typedef void (*TDataHandler)(void* Self, void* Data);

void DoSomething();
{
  ((TDataHandler)(StoredH.Code))(StoredH.Data, SomeData);
}

Warning, this is pseudo code, you should adapt it so that it can compile.
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Re: [fpc-pascal] how to use procedure of object in C

2015-03-10 Thread Jonas Maebe 


On 10 Mar 2015, at 10:40, OBones wrote:


Xiangrong Fang wrote:
However, like in my first mail, if I define THandler a procedure of  
object, it makes easier to SetHandler(AMethod); but how can I use  
that procedure of object pointer in the so?


It works the same, cast the data you receive to a TMethod and call  
the code member with the appropriate parameters. So, in the C  
library do this:


Note that you have to make sure that you declare your procedure of  
object as cdecl in that case, and as a result you'll also have to  
declare all methods that you want to assign to this procvar as cdecl.



Jonas
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Re: [fpc-pascal] how to use procedure of object in C

2015-03-10 Thread Michael Schnell 

On 03/09/2015 04:20 PM, Xiangrong Fang wrote:


can I implement SetHandler in a library written in C, then call h in C?

For inter-language calls you obviously need to to define the calling 
style on both sites. e.g. STDCALL or PASCAL, to make both use 
compatible calling conventions.


I don't know if/how such keywords exist for procedure of object style 
of functions (and hence for the types of the variables pointers to them 
are stored in).


If not you should use a flat calling scheme: on both sites use 
standard (non-object) functions with e.g. STDCALL (adding/extracting 
the Self pointer explicitly on the way, if appropriate). Regarding 
variables for holding (pointers to) such functions they need to be a 
record of a (flat) function pointer plus a Self pointer.


This said, you can't (easily) pass objects to a C library, anyway, as 
the memory management is not synchronized by default. Like with Pascal 
Strings, a e.g. Free will lead into chaos.


-Michael
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Re: [fpc-pascal] how to use procedure of object in C

2015-03-09 Thread Ewald 

On 09 Mar 2015, at 18:43, Michael Van Canneyt wrote:

 
 You must be sure that self is passed in the correct register.
 I am not sure this is the case if you declare it as an extra argument.

It is, as long as the `self` is the first parameter. Same goes for `Class 
Procedure XXX;` kind of declarations (in constrast to `Class procedure XXX; 
static;`).

I don't know how long that is going to last however (since this hidden 
parameter thingy is an implementation detail of the compiler I think). So I 
fully agree: it would be a kindness of the compiler people to confirm this :-)

--
Ewald

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Re: [fpc-pascal] how to use procedure of object in C

2015-03-09 Thread Michael Van Canneyt 



On Mon, 9 Mar 2015, OBones wrote:


Michael Van Canneyt wrote:



On Mon, 9 Mar 2015, Xiangrong Fang wrote:


Hi all,
I define a procedure like this:

type
  TDataHandler = procedure(data: Pointer) of object;

procedure SetHandler(h: TDataHandler); external cdecl;

Now, can I implement SetHandler in a library written in C, then call h in 
C?


IMHO Not without separate assembler code for each CPU.

Michael.

How about using TMethod?

procedure DataHandler(DummySelf: Pointer; data: Pointer);
begin
 // do what you want to do, DummySelf is always nil.
end;

var
 Method: TMethod;
begin
 Method.Data := nil;
 Method.Code := @DataHandler;

 SetHandler(TDataHandler(Method));
end;


You must be sure that self is passed in the correct register.
I am not sure this is the case if you declare it as an extra argument.
It may be so, but compiler people should confirm this. 
I don't think you can take it for granted.


Michael.
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Re: [fpc-pascal] how to use procedure of object in C

2015-03-09 Thread Michael Van Canneyt 



On Mon, 9 Mar 2015, Xiangrong Fang wrote:


Hi all,
I define a procedure like this:

type
  TDataHandler = procedure(data: Pointer) of object;

procedure SetHandler(h: TDataHandler); external cdecl;

Now, can I implement SetHandler in a library written in C, then call h in C?


IMHO Not without separate assembler code for each CPU.

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Re: [fpc-pascal] how to use procedure of object in C

2015-03-09 Thread OBones 

Michael Van Canneyt wrote:



On Mon, 9 Mar 2015, Xiangrong Fang wrote:


Hi all,
I define a procedure like this:

type
  TDataHandler = procedure(data: Pointer) of object;

procedure SetHandler(h: TDataHandler); external cdecl;

Now, can I implement SetHandler in a library written in C, then call 
h in C?


IMHO Not without separate assembler code for each CPU.

Michael.

How about using TMethod?

procedure DataHandler(DummySelf: Pointer; data: Pointer);
begin
  // do what you want to do, DummySelf is always nil.
end;

var
  Method: TMethod;
begin
  Method.Data := nil;
  Method.Code := @DataHandler;

  SetHandler(TDataHandler(Method));
end;

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Re: [fpc-pascal] how to use procedure of object in C

2015-03-09 Thread Xiangrong Fang 
2015-03-10 0:33 GMT+08:00 OBones obo...@free.fr:


 How about using TMethod?

 procedure DataHandler(DummySelf: Pointer; data: Pointer);
 begin
   // do what you want to do, DummySelf is always nil.
 end;

 var
   Method: TMethod;
 begin
   Method.Data := nil;
   Method.Code := @DataHandler;

   SetHandler(TDataHandler(Method));
 end;


​I'm not sure how this works, but it seems that you are deliberately
converting a normal procedure to a method. What I want is exactly opposite
- I want to convert a method to a normal procedure.

If I define the interfact of DataHandler like this:

​TDataHandler = procedure(data: Pointer); cdecl;

It is very easy to use in an so, no matter it is written in C or pascal.

But the problem is, I want to do this:

SetHandler(h);

where h is a METHOD, not a normal procedure​.

Because I want to use the handler wrapped in my Class.

However, like in my first mail, if I define THandler a procedure of object,
it makes easier to SetHandler(AMethod); but how can I use that procedure
of object pointer in the so?

Thanks!


​
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