typed files: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: typed files

New		Line
1	+	## Typed file
2	+
3	+	A typed text file is suitable for processing files of any size. A typed text file consists of individual data records. All records in the file have the same structure. This means that each data record is of the same length.
4	+
5	+	## Set the file and record structure
6	+
7	+	The structure applies to the file type and the record type. The file and data record must have the same structure.
8	+
9	+	``` pascal
10	+	type
11	+	TMemployee = Record
12	+	strName : String[20];
13	+	sinContent : Single;
14	+	end;
15	+	```
16	+
17	+	## Create the file
18	+
19	+	``` pascal
20	+	var
21	+	datFile : File of TMemployee;
22	+	recData : TMemployee;
23	+	begin
24	+	AssignFile(datFile, 'example.txt');
25	+
26	+	// An existing file is deleted and re-created
27	+	ReWrite(datFile);
28	+
29	+	...
30	+	end;
31	+	```
32	+
33	+	## Close the file
34	+
35	+	``` pascal
36	+	begin
37	+	...
38	+	Close(datFile); // closes the file
39	+	...
40	+	end;
41	+	```
42	+
43	+	## Write data record
44	+
45	+	``` pascal
46	+	var
47	+	datFile : File of TMemployee;
48	+	recData : TMemployee;
49	+	begin
50	+	...
51	+
52	+	// fill the record
53	+	recData.strName := 'abcdefghij';
54	+	recData.sinContent := 1700.21;
55	+
56	+	// write the record to the file
57	+	Write(datFile, recData);
58	+
59	+	...
60	+	end;
61	+	```
62	+
63	+	## Read data record
64	+
65	+	``` pascal
66	+	var
67	+	datFile : File of TMemployee;
68	+	recData : TMemployee;
69	+	begin
70	+	AssignFile(datFile, 'example.txt');
71	+
72	+	Reset(datFile); // Set the file pointer to the beginning of the file
73	+
74	+	Read(datFile, recData); // Reads a record from the file
75	+	...
76	+	end;
77	+	```
78	+
79	+	## Read file completely
80	+
81	+	``` pascal
82	+	var
83	+	datFile : File of TMemployee;
84	+	recData : TMemployee;
85	+	begin
86	+	AssignFile(datFile, 'example.txt');
87	+	Reset (datFile);
88	+
89	+	while not eof(datFile) // as long as data can still be read
90	+	do begin
91	+	read(datFile, recData); // read record from file
92	+	...
93	+	end;
94	+
95	+	CloseFile (datFile);
96	+	end;
97	+	```
98	+
99	+	## Position pointer on a data record
100	+
101	+	``` pascal
102	+	begin
103	+	AssignFile(datFile, 'example.txt');
104	+	Reset(datFile);
105	+	...
106	+
107	+	Seek(datFile, 0); // position file pointer at start of first record
108	+	Read(datFile, recData); // read first record into recData variable
109	+
110	+	recData.sinContent := 1602.22; // update record
111	+
112	+	Seek(datFile, 0); // position file pointer at start of first record
113	+	Write(datFile, recData); // write first record back
114	+
115	+	...
116	+	end;
117	+	```
118	+
119	+	## See also
120	+
121	+	- [[File types]]
122	+
123	+	---
124	+	From the Free Pascal wiki, page "typed files", as it stood on 2020-03-02 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).

Back to history