Add and remove data from file

Is t possible to:

Add data to a certain offset in a file without overwriting original data from that offset, thus expanding the file?

Remove data from a certain offset and length in a file, instead of making a new file of the two desired parts of data from the original file?

Thanks!

[330 byte] By [APMadsen] at [2007-12-22]

«« Saving in ComboBox
»» creating label

# 1

This can be difficult to do robustly. What I recommend is that you read the original file into memory, make your changes, and then write it back out. You don't want to be in a situation where, say, you have adjusted the file by creating space at your offset, but your program crashes or the computer turns off or something else happens and your app doesn't get a chance to write the data there. You now have corrupted files.

I'd almost recommend writing the new file to a temporary file location, and then swapping it with your original file. Of course, it depends on how robust you want your application to be.

TimothyNgMSFT at 2007-8-30 >

top of Msdn Tech,Visual Basic,Visual Basic General...

# 2

And reading files into memory is whether it be a text file or a binary file is easy using

My.Computer.Filesystem. (readalltext or readallbytes)

The manipulating the in memory data - by removing , adding or changing items etc. before writing this stuff back to a file using the companion function

My.Computer.Filesystem. (writealltext or writeallbytes)

As tim suggested there are many ways you can make this more robust to ensure that you dont get corrupted files but this way is simple and for small to medium files the file reading and writing may prove to be fast enough. So you get a easy to maintain - simple to debug solution.

spotty at 2007-8-30 >

# 3

Just to add my 2p... when you have the file in memory (e.g., in a string) you can use string.insert to add data and string.substring to remove... :)

weirdbeardmt at 2007-8-30 >

# 4

I would use a StringBuilder (with enough allocated memory) rather than inserting into strings, though - each time you insert into a string, you will create a brand new string (so if your 'string' is 2Mb in size, it'll copy the whole 2Mb to another string). This is what it means when strings are immutable - you cannot change them.

SJWhiteley at 2007-8-30 >

# 5

Well we're talking about files that are anywhere from 0-100 or mor MB og length, so i think that i will have to write new files each time i have to remove or add some data inside.

APMadsen at 2007-8-30 >

# 6

Sure performance may be an issue with files this size and the stringbuilder class may be the best option.

Also remember windows uses virtual memory, so it will page items in an out of memory if you dont physically have 100Mb free in your machine at the time.

Are we talking like a batch process to update this file or are you talking about an interactive application - Is it possible that you could use a database to do interactive parts of the process and then create an export option to output the required format file.

spotty at 2007-8-30 >

Visual Basic Hot Topic

Visual Basic New Topic

Visual Basic

Java / MSDN / Linux Tech / PHP Tech / MSDN DotNet / MSDN TECH / Health Library / Programmers Tech / visual basic Tech / Developer Tech / Ipod faqs / Msdn China Tech

it's Archive about 'Add and remove data from file...'

Add and remove data from file

Visual Basic Hot Topic

Visual Basic New Topic

Visual Basic

Site Classified