Accessing dll within a class

[DelphiDinosaur]

I'm having some trouble accessing a dll from within a class.

Code: Pascal  [Select][+][-]

1. const
2.   DLL_NAME = 'Adder.dll';
3. type
4. TAdd = function(A: byte; b: byte): word; cdecl;
5.  
6. TMyClass = class
7. private
8.   fnAdd: TAdd;
9.   dllHandle: LongWord;
10. public
11.   constructor Create;
12.   destructor Destroy;
13.  
14.   function AddA(A: byte; B: byte): word;
15.   function AddB(A: byte; B: byte): word;
16. end;
17.  
18. constructor TMyClass .Create;
19. begin
20.   dllHandle := LoadLibrary(pchar(DLL_NAME));
21.   if (dllHandle <> 0) then
22.     Pointer(fnAdd) := GetProcAddress(dllHandle, 'Add');
23. end;
24.  
25.  
26. destructor TMyClass.Destroy;
27. begin
28.    FreeLibrary(dllHandle);
29. end;
30.  
31.  
32. function TMyClass.AddA(A: byte; B: byte): word;
33. begin
34.   Result := fnAdd(A, B);
35. end;
36.  
37. function TMyClass.AddB(A: byte; B: byte): word;
38. var
39.   tmpHandle: LongWord;
40.   tmpAdd: TAdd;
41. begin
42.  
43.   tmpHandle:= LoadLibrary(pchar(DLL_NAME));
44.   if (tmpHandle<> 0) then
45.   begin
46.     Pointer(tmpAdd) := GetProcAddress(tmpHandle, 'Add');
47.     if Assigned(tmpAdd) then
48.       Result := tmpAdd(A, B)
49.   else
50.  
51.   end;
52. end;
53.  

[balazsszekely]

@DelphiDinosaur

I'm having some trouble accessing a dll from within a class.

What trouble exactly?  Which part of your code fails? Try this:

Code: Pascal  [Select][+][-]

1. uses dynlibs, LCLType;
2.  
3. var
4.   DllHandle: TLibHandle;
5.   FarProc: TFarProc;
6. begin
7.   DllHandle := LoadLibrary('Adder.dll');
8.   if DllHandle <> 0 then
9.   begin
10.     FarProc := GetProcedureAddress(DllHandle, 'Add');
11.     if FarProc <> nil then
12.     begin
13.       //...
14.     end
15.     else
16.       ShowMessage(SysErrorMessage(GetLastOSError))
17.   end
18.   else
19.     ShowMessage(SysErrorMessage(GetLastOSError));
20. end;

Also on windows the calling convention is usually stdcall not cdecl.

[Zvoni]

Also on windows the calling convention is usually stdcall not cdecl.

Not neccessarily if he's written the dll himself

[systemdesigner]

First of all, hello everyone.
I need your help about a problem in my project; debugging a dll unit, is broken.
In fact, I have been debugging many times before nowamdays. I was amazed to see how well
it was working. But it was broken later on. I always upgrade IDE and now it's the latest.
I think, it is caused by changing the IDE or changing project preferences, but no idea...
I removed the latest Lazarus IDE and replaced with its old copies to catch the problem.
I compiled and tested my old versions with old IDE versions and different preferences.
Although I tried all combinations, I could not find the reason. Unfortunately, no way.
The dll project and main project were always compiled with the same Lazarus IDE copy.
The main calls: "DynLibs.LoadLibrary(), DynLibs.GetProcedureAddress(), DynLibs.TLibHandle".
Then I put many breakpoints onto the "ALibName" unit codes. Just after the LoadLibrary(),
main code calls a method from the dll by an ALibHandle code line. However, it doesn't stop
on any breakpoint anymore. Please inform me for the solution. Thanks.
Now Lazarus IDE is 2.2.6 Win32 on Windows10 64bit.

[cdbc]

Hi
@systemdesigner: We need to see some code...
@DelphiDinosaur: What kind trouble are you having? Have you tried GetMem's
 tip, what did it say?
Regards Benny

[systemdesigner]

Hi CDBC
Does debugging into or putting breakpoint in dll, matter the pascal code!?
Does not it matter with lazarus version, compiling options or project preferences?
I used LoadLibrary etc. as I mentioned...

[Thaddy]

No. If you want to debug a dll, load the dll sources and tell the ide which program is the host. Simple.

[systemdesigner]

Hello @Thaddy.
I have a main prj that loads the lib. Library also have own project, having the "library testlib;" unit.
In the lib prj, Run->Run Parameters->Host Application, I typed the main prj file (...\prj1.exe).
Anyway, it doesn't stop on breakpoint on the lib unit.

[systemdesigner]

No. If you want to debug a dll, load the dll sources and tell the ide which program is the host. Simple.

Could you please describe to me here...?