reading different sections of a text file at a time

[mustakbal]

How can I read only a section of a text file at a time.Say I have a text file of 1000 rows as database and I want to read from row 1 to 200 only, then maybe from 201- 275 and so on.
What is the code that would use if I create a button that says 1-200.

Thanks

[Dököll]

How can I read only a section of a text file at a time.Say I have a text file of 1000 rows as database and I want to read from row 1 to 200 only, then maybe from 201- 275 and so on.
What is the code that would use if I create a button that says 1-200.

Thanks

This is a nicely detailed post, mustakbal!

I will try to see if can find you an example, something may already been posted I'll search there too.

Please stay tuned, welcome!

[Dököll]

Just tried and it works at my end:

(1) Add a command button to your form, add a loop
(2) I have three labels, you can modify, Label1(0), and so on...
(3) You can dimension found, Linenum, and pos, Dim as integer seems to work okay

The result is you get the number of line in the document red through a multiline box (Text1.Text). Sorry this is reading it reverse, could not find a good example

 
Do Until found = 0
   found = InStrRev(Text1.Text, Chr(10), pos, 0)
   If found = 0 Then Exit Do
   Linenum = Linenum + 1
   pos = found - 1
Loop
Label1(0).Caption = Linenum
 

You should also assign values:

 
found = -1    
Linenum = 1  
pos = Text1.SelStart    
 
 

Add a lengthy letter in the Text1.Text mutiline textbox and fire command button, Label1(0) should tell you how many lines are in the document.

There are other ways to do this, please let us know.

[mustakbal]

Thanks Dököll for your offer to help. I have been trying to make the code above work with no success yet. But I still don't see where I am setting the limit of high and low number of rows. By the way I am a newbie also in vb6 ! so you might need to do the step-by-step instructions with me!

When I open a file that has 1000 lines in it and I declare the number of lines as 1000, and then wanted to randomly call different lines, it will be picking them from among the numbers 1 through 1000. Now, how do I set the upper and lower limits (say 200 as the low and 600 as high) and have the program call randomly only from the lines 200 throgh 600.

If I can do that with this code where would the 200 and 600 go in the code.

Thanks in advance.

[Killer42]

You could use any code you like to read the file (there's a simple code snippet to do this in the Articles section - you can find it in the Index up the top of this forum).

Assuming you are reading from the start of the file, all you have to do is count the lines as you read them. If you want to process lines 201-700, just skip each line until your count reaches 201. Then when your count hits 701, drop out of the loop.

It would probably be both faster and more efficient (unless the file is too large) to just read all of the lines into an array. Then you can pick and choose from the array, however you like.

On the other hand, if the lines are all the same length you could open the file in "random access" mode which allows you to just straight to any line, by number. In other words, you could tell VB to open the file, jump to the 384th line, read it, and close the file, without accessing any other lines in the file. But only if the lines are of identical length. (Note that if you did want to go this way you could always pad the lines with spaces or something to make them the same length.

[mustakbal]

O K,Killer42..we are on the right track but please keep in mind that you are dealing with a newbie. The part about : "If you want to process lines 201-700, just skip each line until your count reaches 201. Then when your count hits 701, drop out of the loop." is what I am interested in doing..but how do I set these limits in the progrogram and then have that followed by the program choosing entries at random from this set only (201-700).Does the program have to go through the skipping procedure each time it chooses another random entry or is there a better way of doing that.

That's where I am stuck right now trying to write the code
1- set the limits and
2- have entries randomly chosen from between these numbers.

By the way I have the code for choosing random entries from the whole file but not parts.

Thanks

[1fromOZ]

'Try This
 
'On your Form
' Place a command button called CmdRead
' Place three text boxes called txtMyFile, txtstartline, txtendline, txtReadLine
' Type your file name (including path and the extension of the file) in txtMyFile
' or alternatively type the file name (including path and the extension of the file) in quotation marks inplace of txtMyFile.text like "C:\Data\myFileNametoRead.txt"
' Type first and last line numbers you want to read in txtstartline and txtendline respectively
' Click CmdRead
 
'Unfortunately VB cannot handle fixed field length sequential files like QuickBasic used to
' because of that we can not jump to a location in a file
 
 
Private Sub CmdRead_Click()
Dim startline, endline, currentLine As Integer
Dim LineRead As String
startline = txtstartline: endline = txtendline
currentLine = 0:
If startline < 1 Then startline = 1
If endline < 1 Then endline = 1
 
Close #1: Open txtMyFile.Text For Input As #1
 
Do While currentLine < startline
    If EOF(1) <> -1 Then Input #1, LineRead Else GoTo endFile: 'Check if end of file
    currentLine = currentLine + 1
Loop
 
Do Until currentLine > endline
    If EOF(1) <> -1 Then Input #1, LineRead Else GoTo endFile: 'Check if end of file
    txtReadLine.Text = CStr(currentLine) & ": " & LineRead
    MsgBox CStr(currentLine) & " OK", vbOKOnly
    currentLine = currentLine + 1
Loop
 
Finish:
MsgBox "All Done", vbOKOnly
Exit Sub
 
endFile:
MsgBox "end of File", vbOKOnly
 
End Sub

[mustakbal]

1fromOZ]
This worked great... but can I code a button so that clicking it would set the lower and upper limits as 1-100 and another button as 101-250 and so on. and have this code in the program so that if I wanted to work with 101-250 set I would click the second button.
I think the answer is in your code but I haven't figured it ouit yet.

[Killer42]

Unfortunately VB cannot handle fixed field length sequential files like QuickBasic used to because of that we can not jump to a location in a file

I'm afraid that is simply not true.

VB probably does handle them slightly differently - it's been quite a few years, I can't remember QB in that much detail. But you can open as random (random-access fixed-length record file) and jump directly to any record you want. If you open as Binary, you can jump directly to any byte in the file and start reading.

[Killer42]

By the way I have the code for choosing random entries from the whole file but not parts.

Surely all you have to do, then, is check that the number of the line you are going to retrieve is within the desired limits. You shouldn't need to make any change in the file handling.

Let's assume you have two variables called LowerLimit and UpperLimit, defining the section of the file you're allowed to read. You then decide to go and get line number RequestedLineNu mber...

Select Case RequestedLineNumber
  Case LowerLimit To UpperLimit
    ' Do whatever it is you do now.
  Case Else
    ' Return an error, or whatever.
End Select

You could also have used an IF...ELSE of course. I just happen to like Select Case because of the way it allows you to define a range using the To clause.