Text Only | Text with Attachments

QB64.org Forum

Active Forums => Programs => Topic started by: Dimster on June 14, 2021, 09:49:47 am

Title: Pseudo Random Access to Sequential Files
Post by: Dimster on June 14, 2021, 09:49:47 am
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]
  2. Screen _NewImage(2000, 1000, 32)
  4.  
  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
  23.  
  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.  
  109.  
  110.  


Text Only | Text with Attachments