Reading Certain lines in a text file

[gobblegob]

Hi,
I would like to know how i could read and write in a specific line in a text file with VB6.

eg.

first line
second line
third line

I dont want to read through all lines, I just want to read a certain line as an input and write to a certain line as output.


Thanks
Gobble.

[SonnyH]

Can't do that with text file.......

[WinblowsME]

Here's the code to read in certain lines from a file. As for writing to a certain line in a file, do you want to write to the file you're reading? Give us an example.

   Dim line1 As String, line2 As String, line3 As String
 
   Open App.Path & "\Temp.txt" For Input As #1
      Line Input #1, line1
      Line Input #1, line2
      Line Input #1, line3
   Close #1
 
   Debug.Print line1 & Chr(13) & line2 & Chr(13) & line3
 

[Killer42]

Subscribing .

[gobblegob]

Here's the code to read in certain lines from a file. As for writing to a certain line in a file, do you want to write to the file you're reading? Give us an example.

   Dim line1 As String, line2 As String, line3 As String
 
   Open App.Path & "\Temp.txt" For Input As #1
      Line Input #1, line1
      Line Input #1, line2
      Line Input #1, line3
   Close #1
 
   Debug.Print line1 & Chr(13) & line2 & Chr(13) & line3
 

Thanks for the reply its exactly what i wanted ti know,
Sorry for the late reply but i gave up after getting told it cant be done.
Thanks again,
Gobble.

Thanks for the post mate much appreciated.
Gobblegob.

[Killer42]

Thanks for the reply its exactly what i wanted ti know,
Sorry for the late reply but i gave up after getting told it cant be done.

Never listen to the people who tell you "it can't be done". They might be right, but if you believe them, you'll never find out.

[gobblegob]

Here's the code to read in certain lines from a file. As for writing to a certain line in a file, do you want to write to the file you're reading? Give us an example.

   Dim line1 As String, line2 As String, line3 As String
 
   Open App.Path & "\Temp.txt" For Input As #1
      Line Input #1, line1
      Line Input #1, line2
      Line Input #1, line3
   Close #1
 
   Debug.Print line1 & Chr(13) & line2 & Chr(13) & line3
 

Is there a way i can choose a line to output to?

Dim line1 As String, line2 As String, line3 As String

Open App.Path & "\Temp.txt" For Output As #1
Line Output #1, line1
Line Output #1, line2
Line Output #1, line3

But it doesnt work any suggestions?
Thanks again,
Gobble.

[Killer42]

The statement you want there is Print #1, not Line Output #1.

I believe that what SonnyH was referring to is the difficulty of accessing a specific line in a text file, as opposed to reading or writing all the lines, as you're doing. You see, since the lines can be of different lengths, there's no way VB can tell where any given line starts, except by reading all of the lines up to that point.

When writing to a text file, things are even worse. There's no convenient way to move chunks of a file around. So if you want to write over the top of an existing line, what happens to all the rest of the data that comes after it?

There are ways to work around all of this, of course. But it's worth keeping in mind. In fact an upcoming article in the HowTo's area will show an easy way of playing with a text file in this way. And there are articles there already which demonstrate a couple of ways to read files.

[WinblowsME]

Sub Test()
   Dim file_name As String
 
   file_name = "C:\Documents and Settings\WinblowsME\Desktop\Input.txt"
 
   Call Insert_Line(file_name, 3, "INSERT INTO LINE 3")
   Call Insert_Line(file_name, 5, "INSERT INTO LINE 5")
   Call Insert_Line(file_name, 7, "INSERT INTO LINE 7")
End Sub
 
Private Sub Insert_Line(file_name As String, line_num As Long, str_line As String)
   Dim lines() As String, i As Long
 
   i = 1
 
   On Error GoTo ERROR_HANDLER
 
   Open file_name For Input As #1
      Do While Not EOF(1)
         ReDim Preserve lines(i)
         Line Input #1, lines(i)
         i = i + 1
      Loop
   Close #1
 
   If i = 1 Or line_num > i Then
      Open file_name For Append As #1
         Print #1, str_line
      Close
   Else
      Open file_name & "_TEMP" For Output As #1
         For i = 1 To UBound(lines)
            If i <> line_num Then
               Print #1, lines(i)
            Else
               Print #1, str_line
               Print #1, lines(i)
            End If
         Next i
      Close
 
      Kill file_name
      Name file_name & "_TEMP" As file_name
   End If
 
   Exit Sub
ERROR_HANDLER:
 
End Sub

[Killer42]

Thanks Winnie, looks like a handy routine.

As you can see from this, gobblegob, the only "convenient" way to replace a line in a text file (unless you can guarantee that the new line is exactly the same length) or to insert a line as this code does, is to make a new copy of the file, with the new line in it.

There are quite simple ways to update data inside a file without moving anything around, but if the size of the updated part is to change, then you need some way to move the rest of the data. Making a copy like this is probably about the most common way, as it's probably about the only safe way. ZIP utilities, for instance, do exactly that. If you add, remove or update anything in a ZIP file, the utility simply makes a complete copy of the ZIP archive, with the changes in it. Then it deletes the old copy, and renames the new one.

[WinblowsME]

The code is not very efficient though. I'm thinking that the dynamic array is not needed...

[Killer42]

The code is not very efficient though. I'm thinking that the dynamic array is not needed...

Yeah, it certainly seems as though it would be more efficient to copy directly from one file to the other.

Putting them in an array something like that could be useful way to cache the entire file so you only have to read it once. But the existing code obviously doesn't do so.

[gobblegob]

The code is not very efficient though. I'm thinking that the dynamic array is not needed...

Wow thanks for information you guys have bundled for me very helpful.
Gobble.

[xtianixm]

you can use textstream for that