DLL dynamically load: what changed

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Title: DLL dynamically load

New		Line
1	+	The tutorial shows how a DLL (Dynamic Link Library) is loaded dynamically .
2	+
3	+	The DLL (DLLTest.dll) referred to in the example below:
4	+
5	+	``` pascal
6	+	library info;
7	+
8	+	{$mode objfpc} {$H+}
9	+
10	+	uses
11	+	SysUtils;
12	+
13	+	{$R *.res}
14	+
15	+	// The DLL subroutine
16	+	function funStringBack(strIn : string) : PChar;
17	+	begin
18	+	funStringBack := PChar(UpperCase(strIn));
19	+	end ;
20	+
21	+	// Exported subroutine(s)
22	+	exports
23	+	funStringBack;
24	+
25	+	begin
26	+	end.
27	+	```
28	+
29	+	What should I do:
30	+
31	+	- Define memory
32	+	- A data type must be created that corresponds exactly to the (external) subroutine that is to be imported from the DLL.
33	+	- Reserve memory
34	+	- Memory must be reserved for a variable (data field) to which the above data type is assigned.
35	+	- Memory must be reserved for a handle, to which the DLL handle will be assigned later.
36	+	- Assign DLL and external subroutine and accept the data
37	+	- Call the DLL and assign the handle of the DLL to the handle.
38	+	- The pointer for the variables must be changed to the memory of the external subroutine.
39	+	- The result of the external subroutine is to be accepted.
40	+	- Free all memory
41	+	- The pointer for the variables must point to an invalid memory area again (:= nil) to release the external subroutine.
42	+	- The memory of the DLL must be released again.
43	+
44	+	Integrate, use and release the DLL subroutine in your own program:
45	+
46	+	``` pascal
47	+	uses
48	+	Windows, ...;
49	+
50	+	...
51	+
52	+	Include function funDll : string;
53	+	type
54	+	// Definition of the subroutine to be called, as defined in the DLL to be used
55	+	TfunStringBack = function(strIn : string) : PChar; stdcall;
56	+
57	+	var
58	+	// Creates a suitable variable (data field) for the DLL subroutine
59	+	funStringBack : TfunStringBack;
60	+	// Creates a handle for the DLL
61	+	LibHandle : THandle;
62	+
63	+	begin
64	+	// Get the handle of the library to be used
65	+	LibHandle := LoadLibrary(PChar('DLLTest.dll'));
66	+
67	+	// Checks whether loading the DLL was successful
68	+	if LibHandle <> 0 then
69	+	begin
70	+	// Assigns the address of the subroutine call to the variable funStringBack
71	+	// 'funStringBack' from the DLL DLLTest.dll
72	+	Pointer(funStringBack) := GetProcAddress(LibHandle, 'funStringBack');
73	+
74	+	// Checks whether a valid address has been returned
75	+	if @funStringBack <> nil then
76	+	Result := funStringBack('hello world');
77	+	end;
78	+
79	+	// release memory
80	+	funStringBack := nil;
81	+	FreeLibrary(LibHandle);
82	+
83	+	end;
84	+
85	+	...
86	+	```
87	+
88	+	---
89	+	From the Free Pascal wiki, page "DLL dynamically load", as it stood on 2020-02-13 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

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