Problems accessing a library under MacOS

[ChPr]

Hello everyone,

In an application, I use a library (“libarticles.dylib” in the case of MacOS).

Code: Pascal  [Select][+][-]

1. unit LiensDLL;
2.  
3. {$mode ObjFPC}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Dynlibs, Menus, Utils;
9.  
10. type
11.   TListSousMenu = array of TMenuItem;
12.   TAddMenu = function(var NbFct: Integer): PChar; stdcall;
13.   TEnvoiDirLib = function(Dir: PChar): Boolean; stdcall;
14.   TArticleEnBdD = function(var Ref: PChar; var IndA, Qte: Integer; var PU: Double): PChar; stdcall;
15.   TMaJStock = function(Ref, Qte, QtePrec: Integer): Integer; stdcall;
16.  
17. var
18.   HndLib: THandle;
19.   LibOK: Boolean;              {Indique si la librairie est utilisée et valide}
20.   ListSousMenu: TListSousMenu;
21.   ArticleEnBdD: TArticleEnBdD;
22.   MaJStock: TMajStock;
23.  
24. function InstalleLib(FchLib: String): Boolean;
25. procedure ClickMenuLib(Sender: TObject);
26. function LibereLib: Boolean;
27.  
28. implementation
29.  
30. uses
31.   FntBase;
32.  
33. var
34.   AddMenu: TAddMenu;
35.   EnvoiDirLib: TEnvoiDirLib;
36.  
37. function InstalleLib(FchLib: String): Boolean;
38. var
39.   Fch: String;
40.   Menu, SousMenu: TMenuItem;
41.   i, N, NbM, NoM, PosM: Integer;
42. begin
43.   Fch:= DirEXE;
44.   Fch:= IncludeTrailingPathDelimiter(Fch+FchLib);
45.   {$IFDEF WINDOWS}
46.     FchLib:= Fch+FchLib+'.dll';
47.   {$ENDIF}
48.   {$IFDEF LINUX}
49.     FchLib:= Fch+'lib'+LowerCase(FchLib)+'.so';
50.   {$ENDIF}
51.   {$IFDEF DARWIN}
52.     FchLib:= Fch+'lib'+LowerCase(FchLib)+'.dylib';
53.   {$ENDIF}
54.   HndLib:= LoadLibrary(PChar(FchLib));
55.   if HndLib <> 0 then
56.   begin
57.     Pointer(AddMenu):= GetProcAddress(HndLib, 'AddMenu');
58.     Pointer(EnvoiDirLib):= GetProcAddress(HndLib, 'EnvoiDirLib');
59.     Pointer(ArticleEnBdD):= GetProcAddress(HndLib, 'ArticleEnBdD');
60.     Pointer(MajStock):= GetProcAddress(HndLib, 'MajStock');
61.     if (@AddMenu <> nil)
62.     and (@EnvoiDirLib <> nil)
63.     and (@ArticleEnBdD <> nil)
64.     and (@MajStock <> nil) then
65.     begin
66.       EnvoiDirLib(PChar(Fch));                     {On envoie le Dir de la Lib}
67.       Menu:= TMenuItem.Create(Base.MenuPrinc);
68.       PosM:= 1;                      {Position d'insertion des menus de la Lib}
69.       N:= 0;{AddMenu(0) retourne le nom du menu à ajouter et le Nb de Sousmenu}
70.       Menu.Caption:= string(AddMenu(N));
71.       SetLength(ListSousMenu, Length(ListSousMenu)+N);
72.       NbM:= Base.MenuPrinc.Items.Count;            {Nombre de menus prédéfinis}
73.       Base.MenuPrinc.Items.Insert(PosM, Menu);              {Insertion du menu}
74.       for i:= 1 to N do                             {Création des N sous-menus}
75.       begin
76.         SousMenu:= TMenuItem.Create(Base.MenuPrinc);
77.         ListSousMenu[High(ListSousMenu)-N+i]:= SousMenu;
78.         NoM:= i;
79.         SousMenu.ImageIndex:= i+11;   {11 = dernier indice des des menus fixes}
80.         SousMenu.Caption:= string(AddMenu(NoM));
81.         SousMenu.Enabled:= True;
82.         SousMenu.Tag:= i;          {Mémo de l'indice du sous-menu dans son Tag}
83.         SousMenu.OnClick:= @Base.ClickMenu;  {Affectation de la fonction Click}
84.         Base.MenuPrinc.Items[PosM].Add(SousMenu);       {Installe le sous-menu}
85.       end;
86.       LibOK:= True;
87.       Result:= True;
88.     end
89.     else
90.       LibOK:= False;
91.   end
92.   else
93.     LibOk:= False;
94.   Result:= LibOK;
95. end;
96.  
97. procedure ClickMenuLib(Sender: TObject);
98. var
99. //  Str: String;
100.   Pch: PChar;
101.   i: Integer;
102.   d: Double;
103. begin
104.   case TMenuItem(Sender).Tag of
105.  1: begin                 {Connexion pour consultation, modification de la BdD}
106.       i:= 0;
107.       ArticleEnBdD(Pch, i, i, d);
108.     end;
109. { 2: Str:= '';
110.  3: Str:= '';}
111.   end;
112. end;
113.  
114. function LibereLib: Boolean;
115. begin
116.   FreeLibrary(HndLib);
117. end;
118.  
119. end.

On Windows and Linux, this poses no problem. On Mac OS, it crashes on line 66:

Code: Pascal  [Select][+][-]

1. EnvoiDirLib(PChar(Fch));

with the following error code:

Code: Text  [Select][+][-]

1. "Process stopped with reason : EXC_BAD_ACCESS (code=1, address=0x0)".

Any idea of the problem?

Best regards.

Pierre.

[cdbc]

Hi
You could try: setlenght(Fch,1024); or something that fits memorywise, I think the crash comes from the library writing to an empty string ~ nil; a pchar can't reallocate like a string does. with setlength you preallocate a /buffer/ in Fch.
Regards Benny

[ChPr]

Thank you "cdbc" for this solution. However, it doesn't work. In fact, “Fch” is already allocated (not nil) to lines 43 and 44.

Best regards.

Pierre.

[cdbc]

Oh, yeah I see that now, sorry my bad...
As far as the error-message goes, it seems something in that call, references a nil pointer?!? Mysterious...
Regards Benny