ExitProc: what changed

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Title: ExitProc

New		Line
1	+	# ExitProc
2	+
3	+	With ExitProc, you can assign a procedure that is called at the end of the program; even when terminated by a runtime error.
4	+
5	+	It is recommended to save the old ExitProc and to call it from the new ExitProc.
6	+
7	+	## Example
8	+
9	+	In this example, a file that does not exist is deliberately opened.
10	+
11	+	``` pascal
12	+	program ExitProc_Example;
13	+
14	+	const
15	+	MyExitCode = 123;
16	+
17	+	var
18	+	OldExitProc : Pointer;
19	+
20	+	procedure end;
21	+	begin
22	+	WriteLn('This is the end');
23	+
24	+	case ExitCode of
25	+	2:
26	+	begin
27	+	WriteLn('file not found');
28	+	end;
29	+
30	+	MyExitCode:
31	+	begin
32	+	WriteLn('It was deliberately terminated with ', MyExitCode);
33	+	end;
34	+
35	+	else
36	+	begin
37	+	WriteLn('Error: ', ExitCode);
38	+	end;
39	+	end;
40	+
41	+	ExitProc := OldExitProc;
42	+	end;
43	+
44	+	var
45	+	f : file;
46	+
47	+	begin
48	+	// Save old ExitProc
49	+	OldExitProc := ExitProc;
50	+
51	+	// Assign new ExitProc.
52	+	ExitProc := @end ;
53	+
54	+	// Open a file that doesn't exist
55	+	Assign(f, 'abc.txt');
56	+
57	+	// This triggers runtime error 2
58	+	Reset(f);
59	+
60	+	// Terminate with your own exit code
61	+	Halt(MyExitCode);
62	+	end.
63	+	```
64	+
65	+	# ExitCode
66	+
67	+	ExitCode specifies the error code with which the program terminates. Usually, if ExitCode is 0, the program ended normally.
68	+
69	+	## Terminated due to runtime error
70	+
71	+	In this example, if the memory field is exceeded, the exit code is 201 (range check error).
72	+
73	+	``` pascal
74	+	var
75	+	a : array[0 .. 3] of byte;
76	+
77	+	begin
78	+	OldExitProc := ExitProc;
79	+	ExitProc := @end;
80	+
81	+	// memory field deliberately exceeded
82	+	a[4] := 12;
83	+	```
84	+
85	+	## Forced termination
86	+
87	+	If you force a program termination with Halt(), ExitProc is still called.
88	+
89	+	If you Halt(num), then num is interpreted as an exit code. In this example, the exit code is 123.
90	+
91	+	``` pascal
92	+	Halt(123);
93	+	```
94	+
95	+	# See also
96	+
97	+	- [[AddExitProc]] - Add ExitProc procedure at program end.
98	+
99	+	---
100	+	From the Free Pascal wiki, page "ExitProc", as it stood on 2020-05-19 after a change by FTurtle, 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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