VB.net write to existing text file

I think you'll want to do a loop with an exit point inside the loop. The exit point will fire just after the replacement takes place.  Below is a function that I believe will do the trick...The 'WriteToNewFile' is the only code not provided (I can help with that too if necessary).  The down side here is that you will end up going through the whole file every time, which I know you don't want to do.  But once the line is found the 'ReadToEnd' goes really fast.

For example:

Public Function ReplaceLine(newLine As String, myCondition As String) As Boolean
 
Dim oFile as System.IO.File
Dim oWrite as System.IO.StreamWriter
oWrite = oFile.CreateText(C:\newFile.txt)
oRead = oFile.OpenText(-C:\originalFile.txt")
 
 While oRead.Peek <> -1
       LineIn = oRead.ReadLine()
       If LineIn = myCondition Then
            'replace the line
            WriteToNewFile(newLine)
            
            LineIn = oRead.ReadToEnd()
            WriteToNewFile(LineIn)
            
            oRead.Close() 
            Return True 'This exits the routine
       Else
            WriteToNewFile(LineIn)
       End If
 End While
 
'The line was not found...so
 oRead.Close()
 Return False
 
End Function 
 
'After the function is completed you'll need to archive (or Delete) the original and rename the new file to the original's name.

                                              

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unfortunately neither of these solutions will work as desired due the fact that i will have to rewrite the file.

I need to be able to search inside the file find a line with whatever params i am searching for etc then modify or replace the line with out rewriting the file, reading and writing a large 2 mb+ file dozens of times is very time consuming.

anoymore ideas?

Thanks
Zeus

Have you tried it?  Usually reading and writing pure text is very fast...even with files on the scale that you're talking about.

Unless you impose the same FIXED WIDTH for each line you're forced to rewrite the entire file whenever a change is made.

With a fixed width file you can CALCULATE the byte position of the "nth" line and rewrite data just at that point by moving the file pointer position with the Seek() method.

If a fixed width line is not an option then you either need to deal with the entire file rewrite issue or move to a database driven solution.

What about using a dataset reading the file into it, then adding any additions or changes and writing out the dataset and overwriting the existing data file.

The issue then is that the data file is structured as a csv and the data is group in rows of 3 each line 1,2,3 is different in collumn length and the colum length has no fixed count so in effect one group of data containing 3 rows of relivant data for that group could have from 5 cols upto 40 columns.

Is this a better way of storing and editing large "datasets" ?

Thanks
Zeus

If you have such a huge files, why don't you store the data into a database ?

You can always load your data asynchronous (or in another trhead), so that you can continue with the rest of your application

Hi,

SQLCE has a hug footprint and is way to heavy for devices in my opinion, the data i am working with is already in an existing format so i am trying to figure out a resource friendly way of loading editing and saving the data.

Thanks
Zeus

idle mind could you provide me with a working example of how to replace a line in a text file with your idea above, lets say for instance we have a text file with the lines below

===File begin===
Fox
Jumps
Over the fence
===File end===

how would i accomplish your suggestion above with fixed width etc?

Thanks
Zeus

if someone can show an example of replacing a line in a fxed width file using idle minds idea above
i will happily accept it as a solution.

Thanks
Zeus

I'm working on an example....surprisingly this was actually an easier task in VB6.  In VB.Net we have to deal with different encoding schemes.  The default one actually places a BOM (Byte Ordering Marker) at the beginning of the file which throws off the calculations.  Additionally, the .Net versions of FileGet() and FilePut() don't properly allow a Structure containing a Fixed Width String to be used.  =\

Trying to come up with a reliable way to do it...

Fantastic i really appreciate the hard work?

Thanks
Zeus

Hi Idle Mind,

I have looked all over the net to try and resolve this myself but with no luck, i am now entering the stages of desperation, if you can resolve this a nice bonus will arrive in the form of a paypal care package ;-)

Thanks
Zeus

It's nice that Idle_Mind is doing this for you...it is a big task.  You should let him know if your file is in a fixed-width format or not (ie. each row being broken up in a predictable series of ranges as opposed to being a delimited file).

Hi thanks for the reply,

At the moment the files are just comma delimtted files with no fixed width in place, i will write a little conversion utility to process the files for use on a device.

The main issue being as stated above is that the application i have developed for devices needs to be able to edit very large files without loading them into memory.

I really do appreciate the work and i am also a man of my word i will show my thanks with a little bonus, because although i have experience in varying areas of development the above task is beyond my current knowledge.

Thanks
Zeus

How do i get intouch with a moderator to ask for asistance cant seem to find a PM or Mail button?

Thanks
Zeus

At the top of the thread you'll see a "Request Attention" link (it's in your initial post).  Idle_Mind is one of the very best though...he'll follow through I'm sure (he answers a lot of post and so sometimes it takes some time).  Request Attention will send out a new post for help.

Thanks sl8rz im just under allot of pressure for a solution thanks for the help.

Zeus

Sorry I haven't gotten back to this one yet Zeus...  =\

I basically had no power ALL day yesterday and today I'm running round taking dogs to the groomers/veterinarian to have their teeth cleaned/pulled.  Pile all the "daily" stuff on top of that and I'm pretty busy.  =)

I will say that I had a working version in VB6 long ago but no longer have VB6 on my machines at home here.

.Net keeps changing the encoding of the file on me and throwing a BOM (byte order marker) at the beginning which is messing up the calculations.  The closest I came had all the lines mashed together as one long string...not easy on the eyeball but it did allow some edits.

Still messing with it...

Hi Idle mind

Thanks for the feedback, and im sorry to keep posting, dont mean to add pressure but it appears you are my last hope as stated above my knowledge in this area is minimal.

Sorry to hear about the outage nothing worse than not being able to get your email lol :-)
I look forward to hearing from you.

Lots of thanks
Zeus