Pseudo Random Access to Sequential Files

[Dimster]

I am absolutely sure someone out there has done this before and likely better than the algorythm I'm placing here but it was just one of those AHA moments when Novarseg pointed out Seek #1,1 placed the pointer back to the beginning of a Sequential file. You have no idea how often I read that in the past and it never twigged to me that is was useful. I have been Opening and Closing the sequential files to get back to the beginning and the program slowed down so much it was ridiculous. I have just watched FellippeHeitor's recent video and he also points to Seek #1,1 as a useful tool in working with Sequential files.

So here is the simple program which appears to give Random Access to multiple Open Sequential files. The first thing to point out is, I had to convert the name of each sequential file to the same name and add a number to the end of the file name so I could open all 25 files quickly (or quicker than Opening all 25 with unique names one at a time). Then I have a loop there that captures the Last Record value for each of the 25 files. Helps with catching the End of File error but not necessary is you already know how many entries you have in your sequential files.

A true Random Access moves it's pointer forward and backward whereas this coding doesn't do that but gives the appearance that it does. 

Code: QB64: [Select]

1. Cls
2. Screen _NewImage(2000, 1000, 32)
3. _FullScreen
4.  
5. $Color:32
6.  
7. Dim Shared RecordTot(1 To 25)
8. Dim Shared Record
9. Dim Shared FileNum
10.  
11. File$ = "DataFile"
12. ext$ = ".bas"
13.  
14. For y = 1 To 25 '                       This For Loop finds the last record in each of the 25 DataFiles
15.     FNum$ = Str$(y)
16.     FileName$ = File$ + LTrim$(FNum$) + LTrim$(ext$)
17.     Open FileName$ For Input As #y
18.     Do While Not EOF(y)
19.         Input #y, RecordValue
20.         RecordTot(y) = RecordTot(y) + 1
21.     Loop
22. Next
23.  
24. Cls
25. Do
26.     Color Orange
27.     Print
28.     Print "To Exit Select 0 for either the File to access or the Record number to display"
29.     Print
30.     Color White
31.     Print "Which File would you like to access: Note Files are Numbered 1 to 49";
32.     Color Brown
33.     Input FileNum
34.     Color White
35.     Print "What Record number would you like to find ";
36.     Color Brown
37.     Input Record
38.     Color White
39.     If FileNum = 0 Or Record = 0 Then End
40.  
41.     RecordSearch
42.  
43. Loop Until Record = 0
44.  
45.  
46.  
47.  
48. Sub RecordSearch
49.     '
50.  
51.     If FileNum > 25 Then
52.         Print "DataFile";
53.         Color LightGreen
54.         Print FileNum;
55.         Color White
56.         Print " there are only ";
57.         Color Red
58.         Print "25";
59.         Color White
60.         Print " Files in the Data Base ";
61.         Color LightGreen
62.         Print "DataFile "; FileNum; " can not be accessed"
63.         Print
64.         Color Orange
65.         Print "Press any key to continue"
66.         Sleep
67.         Color White
68.         Exit Sub
69.     End If
70.  
71.  
72.  
73.  
74.  
75.  
76.     If Record > RecordTot(FileNum) Then
77.         Print "DataFile";
78.         Color LightGreen
79.         Print FileNum;
80.         Color White
81.         Print " has only ";
82.         Color Red
83.         Print RecordTot(FileNum);
84.         Color White
85.         Print " Records so Record #";
86.         Color LightGreen
87.         Print Record; " can not be accessed"
88.         Exit Sub
89.     End If
90.  
91.  
92.  
93.  
94.  
95.     Seek #FileNum, 1
96.     For x = 1 To Record: Input #FileNum, RecordValue: Next
97.     Print "Record Value is ";
98.     Color LightGreen
99.     Print RecordValue
100.     Print
101.     Color Orange
102.     Print "Press any key to continue"
103.     Sleep
104.     Color White
105.     Cls
106.  
107.  
108. End Sub
109.  
110.