Basic Pascal Tutorial/Chapter 2/Files: what changed

Revision 1 to 2. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		2D - Files (author: Tao Yue, state: changed)
2	2
3	3		Reading from a file instead of the console (keyboard) can be done by:
4	4
5	5		``` pascal
6	6		read(File_variable, Argument_list);
7	7		write(File_variable, Argument_list);
8	8		```
9	9
10	10		Similarly with `readln` and `writeln`. The output is stored into the variables named in `Argument_list`. `File_variable` is declared as follows:
11	11
12	12		``` pascal
13	13		var
14	14		...
15	15		Filein, Fileout : text;
16	16		```
17	17
18	18		The `text` data type indicates that the file is just plain text.
19	19
20	20		After declaring a variable for the file, and before reading from or writing to it, we need to associate the variable with the filename on the disk and open the file. This can be done in one of two ways. Typically:
21	21
22		-	~~`reset(File_variable, 'filename.extension');`\~~
23		-	~~`rewrite(File_variable, 'filename.extension');`~~
	22	+	```
	23	+	reset(File_variable, 'filename.extension');
	24	+	rewrite(File_variable, 'filename.extension');
	25	+	```
24	26
25	27		`reset` opens a file for reading, and rewrite opens a file for writing. A file opened with `reset` can only be used with `read` and `readln`. A file opened with `rewrite` can only be used with `write` and `writeln`.
26	28
27	29		Turbo Pascal introduced the assign notation. First you assign a filename to a variable, then you call `reset` or `rewrite` using only the variable.
28	30
29	31		``` pascal
30	32		assign(File_variable, 'filename.extension');
31	33		reset(File_variable);
32	34		```
33	35
34	36		The method of representing the path differs depending on your operating system. Windows uses backslashes and drive letters due to its DOS heritage (e.g. `c:\directory\name.pas`), while FreeBSD, macOS and Linux use forward slashes due to their UNIX heritage.
35	37
36	38		After you're done with the file, you can close it with:
37	39
38	40		``` pascal
39	41		close (File_variable);
40	42		```
41	43
42	44		Here's an example of a program that uses files. This program was written for Turbo Pascal and DOS, and will create file2.txt with the first character from file1.txt:
43	45
44	46		``` pascal
45	47		program CopyOneByteFile;
46	48
47	49		var
48	50		Mychar : char;
49	51		Filein, Fileout : text;
50	52
51	53		begin
52	54		assign(Filein, 'c:\file1.txt');
53	55		reset(Filein);
54	56		assign(Fileout, 'c:\file2.txt');
55	57		rewrite(Fileout);
56	58		read(Filein, Mychar);
57	59		write(Fileout, Mychar);
58	60		close(Filein);
59	61		close(Fileout)
60	62		end.
61	63		```
62	64
63	65		---
64	66		From the Free Pascal wiki, page "Basic Pascal Tutorial/Chapter 2/Files", as it stood on 2022-08-20 after a change by Kai Burghardt, 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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