File I/O And Registry :: Random Access Files In .NET?
Nov 2, 2009
how to read and write random access records in .NET. Now I know random access files are dead and the response on every query I found with google/bing/yahoo searches was don't use random access use Binary serialization but I can not. I have a situation where I need to read and modify 256 byte records in a file that is used by another application.
Now for a bit of background the file is made up of 27 fixed length records of 256 bytes. Each of the records has a separate structure consisting of 30-120 fields. The proplem I am having is I can create the record structures but when using the FileGet method I am receiving an error. Now I have found samples that showed the same format I am using that claim to work.
The error I am getting is Option Strict On disallows narrowing from type 'System.ValueType' to type 'ProgramName.ModuleName.Record' in copying the value of 'ByRef' paramater 'Value' back to the matching argument.
The basic layout (simplified) is as follows:
Code:
Structure Record
<VBFixedString(6)> Public SomeParam as String
Public SomeNumber as Short
[Code]....
Now the overloads for FileGet show all of the data types including Object. But I have tried various methods to retreive the 256 byte record but without success. Do I have to actually read each of the several hundred fields of the structure one by one? Or am i overlooking something (I have been known for this in the past)
Or (and I'll kick myself if this is the only way) do I just have to set option strict Off in the module and the code as above will actually work.
I would love to be able to just ditch the random access file but I have to keep it for compatibility with several other applications at this time.
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Jan 7, 2009
I am writing a program to calculate Pi to several hundred billion decimal places and this will require lots of GB of memory. I wrote a test program in VB2008 that saved the first 16 digits of Pi (without the decimal point) to both a text file and a random access file, just to be sure it was outputting the numbers properly. For reference the first 16 digits of Pi are:
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Sep 6, 2008
I'm new in vb.net (application). I need to access files or browse files using vb.net. Does anyone knows how can I do it?? I can use the listview??This is the process:I have a form and I need to browse folders and drivers (C drive/network drive...) in the same form. But how can I do that, how can I display the icons, file, etc. and open it in listview or any control in vb.net.
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Jan 21, 2009
Error is coming Registry Access is not allowed.While Opening a Key.
Code:
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
NewDelete("HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun", "Sonia")
End Sub
[CODE]...
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Jan 24, 2009
I am a total noob to VB and am only doing an A-level in computing. i'm using VB 2008 express edition am trying to make a windows form application which picks a random file from a folder and displays its contents in text boxes when a button is clicked.
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Feb 28, 2012
I have managed to learn a little of VB 2008 but I'm still struggling. I managed to convert one VB6 program to VB .net but all the file IO in it is sequential access.I'm trying to convert a VB6 program to .net. This program uses almost entirely random file IO.In one of the books I have, I found an example which, with a minor mod worked. I tried using that code to modify my program and it does not work. In my code, the FileGet results in the obj containing null strings. Yet in the sample program using the same structure, the obj contains actual data.The file is being opened because the record count is calculated correctly [iUpper = LOF(F_Trk) / TrkLen].
I used a Type in VB6 which I converted to a Structure in VB 2008. The function in which the problem occurs is below as well as the Structure declaration and the Function it calls (PAB) which is a derivation of the PathAddBackslash API call.Is there an easier, more efficient way to achieve the same results in VB .NET?[code].....[code]......
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Jul 27, 2011
I am trying to convert a VB5 program to VB2010 so that I can continue to support it on my new PC. My copy of VB5 was an upgrade from VB3 which was an upgrade from VB2 which came on floppies, so I can't just install every preceding version as my new PC doesn't have a floppy drive.I have accepted that I will have to design all the forms from scratch (whatever happened to twips?) and will have to go through the thousands of lines of code line-by-line, but I have hit a brick wall when it comes to random access files. One such file is defined in the Declarations section of Module1 thus:[code]....
I soon found I had to change Type to Structure, but then in the declaration of transrec, transtype acquired a wavy blue underline with the error message: "'transrec' cannot expose type 'transtype' in namespace 'Treasurer_2010' through module 'Module1'.So if I can't use the structure in the module in which it is declared, where can I use it?
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Oct 30, 2010
I have 15 years' worth of files (approx. 10,000) that were created using VB6 structures and stored using the random access method. I am trying to write a conversion routine that will read the old structures and put them into a new format that is more compatible with the .net environment. I have not been able to successfully read any of the old files using the tools available in .net. Each file starts with a header record structure. The header record tells me how many tags are in the file. The next record (ie record number 2) is the first tag pointer record in the file.
There are num_of_tags of the pointer records. Each pointer record has the string that holds the tag's 'literal name and two long integers that tell where in the file this tags records are. Those actual records are stored as History data structures, [Code]
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Sep 6, 2010
how do you save data stored in an array of records (structure) to a text file using StreamWriter? I currently have
Private Sub btnSaveToFile_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSaveToFile.Click
Dim sw As New StreamWriter(New FileStream("EmployeeDetails.txt", FileMode.Create, FileAccess.Write))
For Each record As EmployeeType In employees
[code]....
but it doesn't work. My array is fixed and currently has 3 elements (for testing purposes). If I enter two records and add these to the structure I get the following data saved to the text file:
123,helen,66000
879,john,89975
0,,0
How do I stop unused elements of the array being included when writing to file? Should I use a dynamic array instead and if yes, how do you use dynamic arrays with structures?
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Dec 11, 2011
I wrote a program to download and play AVI files the files are large in size and long time wise. I have the files playing as they are being downloaded but i can't see how long the file is or seek reliably. i was reading that the AVI headers are in the last 512kb of the AVI file *why would't they put it at the start* lol so my question is is there a way to download the last 512Kb of the file i'm downloading. i have the Bytes Read and Length of the file while its downlaoding i'm just not sure where to go from there, or how to do it atleast. If i had the length in time of the Avi file i could set the trackbar to be able to seek properly. or if someone has an idea how i could get the time of the video by using fps and some math i could prob do it that way too but idk how i would tell how i can find how many kb are in the fps i'm sure it changes so think that way is't going to be reliable. how to get the last 512kb would be the best option not sure if it can be done even.
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Jan 16, 2012
I'm trying to convert an old Quick BASIC program to VB.Net. There doesn't appear to be any direct replacement for the old file statements. Building a database seems like overkill for my simple needs.
How can I do the following in VB.Net?
OPEN "test.dat" FOR RANDOM AS #1 LEN = 20
FIELD #1, 10 AS a$, 10 AS b$
LSET a$ = "One"
LSET b$ = "Two"
PUT #1, 1
GET #1, 1
PRINT a$, b$
CLOSE #1
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Jan 24, 2009
I'm working with random access files. I created a module and in it put the
Structure PersonData
Dim Name as String
Dim Age as Integer[code]....
The problem is strange... it will let me input string lengths of 3 for Person.Name and Person.Description and it will save correctly, however, the moment I try and lengthen the string (or even if it's longer than 3 to begin with), I get a 'bad record number' error.
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Apr 19, 2011
I have recently decided to give .net another chance, but i have a few questions about it before i get really into it. RE: Files, I use random access files to store data as opposed to databases (namely i don't see the need for a database for storing so little information(records <200 max) knowing that it is an older system and less "cool" i don't care...) Will vs2010 express read, write to random access files? Would it be done kind of like vb6 (which is my current vb version)? I will be needing to print the text of rich text boxes, is vs2010 express capable of doing this?
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Feb 9, 2009
I am writing a backup program that zips files. Using some sample code I have the following that creates a zip file. Problem is it does not get any subdirectories or files. Where am i going wrong?
Dim azFileNames() As String = Directory.GetFiles(SourceFolder)
Dim objCrc32 As New Crc32()
Dim zipStream As ZipOutputStream
[CODE]...
Alternativley, there is another component to the zipping dll that I could probably bypass the above altogether. It is: FZ.CreateZip(DestFile, SourceFolder, True, "", "") Where DestFile is (Output stream as system.io.stream). I'm trying to read all the files, directories, sub dir and files, etc from a specific location, let's say 'My Documents' into Destfile in which the FZ.CreateZip zips the file. FZ is FastZip which is from icsharpcode.net. They have c# examples, but that's greek to me. I'm trying to just learn VB!
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Mar 27, 2009
I've got an app which uses a background worker to copy files. It works fine but some files are quite large and it "appears" as though the app isn't doing anything. Is there an alternative to the File.Copy method of copying files so I can report on the progress of individual file copies, like the percentage complete?
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Jun 2, 2009
Looking for an idea of where the best place to keep files for a program. I use them frequently and they interact with the program directly. I want to place them in a place where they won't be easy to find if someone is just cruising thru the directories. Any ideas?
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Jan 19, 2009
Is there a way to get a list of files in a certain directory and then put them in a context menu strip then when they are clicked have the program open the file. I'm trying to make a flash player that can show the list of flash files and when you click the file path on the context menu strip it will play from that file. Here is what I have:
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
OpenFileDialog1.Filter = "Shockwave Flash Objects (*.swf)|*.swf|All files (*.*)|*.*"
[code].....
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Jul 24, 2010
I should mention that I'm mainly concerned with Random files.Which is the best method?
1.) Open file, manipulate data and immediatly close the file. (Which means doing this alot everytime data needs to be read, edited, deleted, or saved)
(2.) Open the file when the app starts and let it open for data manipulation until it's time to close the app at which time the file would be closed.
I was always taught option 1. The main reason at the time was to cut down on the chance for data corruption in the file or an outright loss of the file due to outside circumstances like power failure.
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Jan 25, 2012
I'm programming a small windows app that allows the user to fill out some fields and then creates and runs a batch file based on their entries. The program works, but it doesn't.The program creates the batch file just fine but when it tries to run the batch file, it gets errors in the cmd window saying it cannot find the scripts the batch file is trying to call. What's confusing me is that if I take the batch file the program created and run it myself, it works just fine so I know it is not the batch that is the problem. My best guess is that there is some security setting for vs.net that I've overlooked but I am only an "every once in a while" programmer so I really don't know where to look. Additionally after running the batch, the program is supposed to delete the batch file but that fails as well with the message that it cannot find the batch file, the same batch file that it had just created and run.
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Dec 10, 2008
have just started vb .net and im working with the 2005 edition, but i would now like to make a program that i can use at home that will alter files names,Bassically where i rip cd's to put them onto my mp3 player they are always given a name starting with 01. etc, what i would like is a small bit of code that uses a while or for loop to go through every file in the folder and remove the first three characters.
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Sep 25, 2009
I'm trying to keep the oldest file and move the new ones to a different directory
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Sep 1, 2008
Alright this is what im working with. Im Working with vb.net 2003.I have (X) amount txt files in "C:Marble".In each txt files there are 3 lines.I want to read the first line of each txt file and display them in a listbox. [code] Things i need to Find:
-1 How to tell how many files are in a folder
-2 How to create a loop were it reads the first line of each file in that folder
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Apr 24, 2009
An application that my company uses stores report files with a .dat extension for use with their software. These files can be opened in notepad and the basic report information can be seen as text. I am attempting to write an app that opens and reads data from these .dat files and displays it in a checked listbox. My hangup thus far is that I can't figure out how to read the data from the .dat files since they are not .txt files. Can anyone point me in the right direction?
[Code]...
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Jun 2, 2010
I know how to get a list of files in a local Windows machine's specific directory:
Dim dirInfo As DirectoryInfo = New DirectoryInfo("C:Temp")
Dim fileListing() As FileInfo = dirInfo.GetFiles()
But how do I use this class for a mainframe system where user ID, password and 'change directory' command are needed?
When I attempt to just access the server without credentials and just do the Windows version and use the syntax "\server_nameAUTO:RPTS.", where 'AUTO:RPTS.' is the mainframe directory name I get the following error: "The given path's format is not supported."
When I just use '\server_name' I get: "The UNC path should be of the form \servershare."
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Aug 28, 2009
I am using zipforge.net to archive files in a small backup program I am creating. Everything works fine however if I try to archive a large number of files the process of zipping them gets slower the further along in the job it gets.
Example: I have a directory that contains a little over 100,000 files in it. Each file is only about 200k of text. When I use the zipforge zip class it starts zip'ing very quickly but as it gets about 40% of the way through the directory it starts to slow down... at about 60% its working at a snails pace.
Memory usage for my solution also goes up proportionate to the archive file size as it grows. Currently it takes around 26hours to backup this directory which only contains 4 gigs worth of information.
If I use a program like winzip I can zip the folder in less than an hour. I am thinking there has to be a way to write to the end of the zip file without having to open it every time or without keeping it open. My backup software scans the specified folder and writes each file path and name into a text file. Then it reads the text file line by line and passes the path + file info to the zipforge addfile().
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Oct 19, 2011
Years ago when coding with VB6 and earlier, I used a file open command to create, read, and write a file that made it easy to store useful information.I believe it was binary and you wrote/read the data to a specific line in the file. When you opened the file with something like notepad, it just showed random ascii chars. When I needed a line of data, I could specify what line to load it from.
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Apr 28, 2010
i have a problem where i've hard coded the file path of an access database i'm using with a VB.net program. this means that if i publish the program the database doesn't publish with it and i have to "ship" the program with the the database file separately and create another form so the user can say where the file is held. i don't want to do this.is there any way to get the access database file to publish with the program and then access that file path by code? for example the database file is held in the same folder as the installed program and then is accessed by code so there is no need to use a specific file path.
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Nov 20, 2009
For a project, I need to extract all the frames of an AVI video. This I have accomplished by with free program. The problem: it took a 30 second clip and spit back 5400 some frames, and the image only changes every 20 frames or so. I really only need about 270 frames, but I didn't want to go through each one manually. So, I wrote a small program using Visual Studio 2008 and VB to open each image in binary and compare it to the one before that. If there is a discrepancy of more than 55000 (to accommodate slight errors in capturing), it leaves the file be. If not, it deletes it.
After much troubleshooting, I got it all to work. I ran it on the directory containing the images, but when it finished, only the first image remained. I checked into it, and found that the FSO loop I have set up to loop through each file was pulling the files in apparently random order. It will give me the image "bg(01).bmp" and then immediately "bg(1362).bmp" and so on. And the order changes every run.
I tried setting up an array to generate a list of all the files and then sort them, so I could pull off the name of the file, then the next one, ect. but it took over 3 hours to finish processing the array, and then It was using a huge chunk of RAM.Is there some way to "force" vb to pull off files in alphabetical order? here is my, code, it belongs with a form. fPath is a global variable, simply pointing to the source directory.
[Code]...
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Jun 18, 2009
im looking for code to copy the files from the floppy drive to a removable drive on the computer.For example:
Copy A:contents to Z:contents
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Mar 28, 2011
I'm trying to copy multiple files from a directory, put them into an array, then copy just the 30 newest files(I haven't coded the 30 newest loop yet). I added a list box to the following code just to ensure the all the files are storing into the array properly... they are. When it try's to copy, it renames the first file to .log, then tells me that the .log file already exist. How do I get it to copy and keep the source file name in the destination folder Eventually I'll loop this and grab only 30 of the files.
Here's the code I'm playing with:
Private Sub transferButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles transferButton.Click
[code].....
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