File I/O And Registry :: Binary File Primer - Read The Nth Record Without Reading The Whole File?
May 4, 2009
I need to write data to a file, preferably in binary format, but I am unaccustomed with the concept. Where's the easiest place to get the basics? I could come here with a specific need, but I'm at the point right now where I am more willing to work within the confines of keeping it simple.
Here's what I know:
1. how to open a new file
2. how to specify the record length
3. how to close the file
Some specific questions:
Does the record length have to be constant throughout the file?
Can I read the nth record without reading the whole file?
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Jun 14, 2009
I've gone through about 16 hours and two packs of cigarettes trying to figure this out. First a little background. I was using 6.0 up until 2004 when I went to prison. I'm out now, and trying to relearn the trade, using VS 2005. I'm currently porting some 6.0 code from another project, SpyCast Webcam Studio, into VB 8.0. It's disheartening, to say the least. None of the old built-in subs/functions work anymore, so I have to scour the forums to relearn each and every function.The section I'm doing now takes a snapshot from the webcam (Video API --> PictureBox --> Save as Jpeg), then upens the file to upload it to the server via HTTP POST. I've been using this code in SpyCast for years with no trouble, but I spent many hours trying to piece together the right code to open the binary file to read its contents. I pieced together two methods I found around the forums, one using FileStream() though the code I found wasn't for binary files, even though it said it was, so that code doesn't really work. Method two uses Microsoft.VisualBasic.FileOpen() and works better.
Here's the kicker. By the time I run through the rest of the rigamarole of uploading the file, by the time I read it on the webserver, it's *slightly* corrupted. It's a valid Jpeg, no errors, but the picture looks like when I use to watch the Playboy Channel when I was a kid scrambled with weird colors and whatnot. [code] Each "chunk" is basically one "line" of the file. It looks like a single LineInput() return is the text between two carriage returns. Am I correct? I tested this with a flat text file, and it looks true. However, That one input line returns the text or data with the carriage returns *stripped*! ***?!? =( Fine, I have no problem adding my own vbCrLf to each LineInput(), if I were opening text. but this's binary. A character could be Chr(10) or Chr(13), both of which are removed from the original file contents.So I could very well need to use something other than LineInput(), but I haven't found any other examples on the web using this method.
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Oct 3, 2010
To read a record in a binary file in VB^ I would define a type with all the fields specifying strings as STRING * whatever the length of the field was.
For example:
Type Record
Field1 as string *15
Field2 to as string * 20
Field3 as String * 10
field4 as byte(10)
End Type
Dim filerecord as record
I would the open my binary fiel and do a Get#1,, filerecord
The record would be read and all the fielsd would be in place.
Now with the new Structure we cant dimension an array in the Structure And wjhen declaring strings we can't specify the length.
I tried to create structire and use a stream binary reader. and just read afixed number of bytes into the type, The program says it canvert bytes to my fiels.
So how do I do this. Or has Microsoft in their infinite wisdom left no way to do this.
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Apr 26, 2010
I used to read a binary file by formatting a record type and then using the Get command to get the data. What is the equivalent in VB.net?
Code:
'In Module.bas
Public Type recordtype
dist As Single
[Code].....
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Jan 11, 2011
i need to read binary file and in this file found the string and replace it with other one and save the file afterwords. I found many example to read binary, but to find and replace is for me mistery.
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Mar 13, 2010
how I could check if a certain file is in text or binary format?I'm using VB.Net 2008 Express.
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Sep 19, 2010
I want to be able to able to read the dimensions of a TIF image without loading the entire file.
PS Using Visual Basic 2008 on Vista64.
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Oct 23, 2011
however, I am stuck at BinaryReader.actually this is what i am trying to acheive through VB.NET.say for the following file type :
JPG file = FF D8 FF E0
BMP file = 42 4D BE 4E
PNG file = 89 50 4E 47
GIF file = 47 49 46 38
the above are the 4-byte headers in Hex(raw) I need to read these headers of any given file using OpenFileDialog using Button1_click event,on selection of any given file(*.* filters ON)it should use the BinaryReader and look for only 4-bytes starting from offset 0, and it should not go to EOF marker (-1).and have a variable to hold this 4-byte header value, to run this in a database table which will check the same header value in the table and would display the corresponding extension of the file. from the table.
I can do this using case, if then...etc.however, I have to do it using Database and also i need to check for testing purpose to use MsgBox() to display this variable which is holding the 4-byte header.however, the MsgBox doesnt allow anything other than String.
PS: I tried studying the methods like:
FileOpen/Seek/Peek/ReadBytes().
but still not sure how to get them work.
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Sep 7, 2008
I have a binary converter I am attempting to build and want to read and convert the InputTextBox(alphabetical characters) letter by letter however all I have so far is one letter at a time
Image here is the code I have so far:
Code:
Public Class ConverterForm
Private Sub OpenToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OpenToolStripMenuItem.Click
[Code]....
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Nov 5, 2010
friend of mine has no HTML knowledge so I'm attempting to write a program that replaces certain parts of a html file to suit his needs.I've edited the HTML file and marked certain parts with "tags" like this:
#IMAGEURL1# I have a textbox where he can copy + paste an image URL and hopefully the #IMAGEURL1# is replaced with the contents of the textbox.
So can someone please enlighten me to-as how to open a HTML file (there's no textbox to display the contents just yet, I'll add one if needed), find the specified text and then replace it with whats in a textbox.
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Jun 14, 2011
I am trying to import a TAB (NOt comma) delimited text file into a DataGridView. The following code works fine if I have a comma separated file. All I have to do is change the FMT to "Delimited".It just does not work with FMT=TabDelimited. All columns are read into single datatable column. The text file is ANSI text and I have double checked to make sure Tabs are tabs and not spaces, even exported a sample Tab Delimited file from Excel.Can this even be done using Text Driver? [code]
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Nov 19, 2008
I'm new to Visual Basic. I'm trying to get this code to read a .txt file line by line. If the only thing that the line says is "B" it should add one to the intTotalBoys integer and so on with G for Girls, F for Fathers, and M for Mothers. I'm not sure why it won't work. [code]
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Oct 28, 2009
I would like to read from file, and ignore lines that start with --. I know how to read line by line but i just need to ignore those lines.
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Jul 5, 2009
So I need to write out an object to a text file as well as read in objects from text files.How do I accomplish this? This is the code i've used to read and write just simple lines of text. Is there a small modification to this or just a different function i use to read in an entire object?
Code:
Dim path As String
path = "Security.txt"
[code].....
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Jul 17, 2010
I have just recently been using VB 2010 after using VB5. I have noticed a lot of changes. The problem I have is that I wish to open and save text files to and from arrays in the background. I've attached what I would do in VB5. I have searched around, but all the examples I find use a Textbox instead of an array. Can anyone show me how I can do this with VB 2010?
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Jan 31, 2009
I've had a bit of a look around the net and on the forums but I've yet to find an answer to my question. I've got Visual Basic 2008 Express and I'm trying to write some registry entries, I can write strings fine just using
[Code]...
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Mar 21, 2010
I need to implement a routine to read a plain text file, BUT that file has a predefined format.The file format is as follows:
Quote:
<FILE_PROPERTIES> 'The "< >" also appears
Propertie1="String" 'It's possible to have spaces after or before the "="
Propertie2="String"
Propertie3="String"
PropertieN="String"
[code]....
Is there any Windows API Routine to read something like that?Or could you point me an URL where something is implemented?I don't want a procedure to read the file line by line and comparing them with Line Input because blank spaces, empty lines and comments starting with " // " may appear too, and I don't want to take them into account, but also I need to save changes to the file, but only to the modified section, without having to read the whole file, and re-write it completely.
Binary access can't work, because I don't know what's the size of each "section", since the number of elements into it can change.
I need something like the "ReadINI" Windows API Procedure, but allowing me to read the "[XXX]" sections headers, and also the "<XXX>" file title header.
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Aug 12, 2010
Before I begin I would like to mention that I am not a noob in VB, it's just I've never had to do anything this complex before. Basically what I want is to have a program that you can load a txt file in, have it copy key words, and paste it in a textbox so I can use it later on. So in this text file, there is a bunch of info, but I am only needing a certain part. Here is an example of a text file (actually a .dat file, but is easily read):
[Code]...
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Aug 14, 2010
I am in the process (slow process) if learning vb.net by trying to create a simple application that will read and write (save) chosen information to a text file. The application has text boxes (name, email address, etc) and I want to read information from certain lines in the text and place in the given text box.
Code:
Dim StreamToDisplay As StreamReader
StreamToDisplay = New StreamReader("C: esting estfile.txt")
TextBox1.Text = StreamToDisplay.ReadLine()
StreamToDisplay.Close()
Currently it's reading the first line of text (which is "[username]").
Text file (testfile.txt) is attached
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Oct 5, 2004
I have read a log file which is being used by a process. I could open the file in notepad or similar applications. The log file is not written by my application.
File.Open or streamreader gives me the following error: "An unhandled exception of type 'System.IO. IOException' occurred in mscorlib.dll. Additional information: The process cannot access the file "E:parkvbproject1.NETinsystem_log" because it is being used by another process."
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Oct 30, 2009
i created a text file with some employee data in vb 2005, on my form i i have a bunch of textboxes and a combobox. i can load the employee numbers manually into the combobox but want the employee details to show in the textboxes when selecting the different employee numbers. i declared a structure with the various fields and a reader to read the text file. here is where i am stuck. my code thus far:
Public ABCStreamReader As StreamReader
[Code]...
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Jan 21, 2009
I'm currently working on an app that grabs listings from a craigslist search (by saving the RSS feed from the results page as an XML file, and then reading it). However, I'm hitting an error.I have the code below in my Form1_Load event:
Code:
My.Computer.Network.DownloadFile("http://greenville.craigslist.org/search/sss?query=ipod%20touch&format=rss", "C:UsersBillDocumentsCLtemp.xml")
Dim CLsr As New System.IO.StreamReader("C:UsersBillDocumentsCLtemp.xml")
Dim CLxr As New System.Xml.XmlTextReader(CLsr)
[code].....
Basically I'm grabbing the RSS feed from the web [URL] currently just a test search for iPod touch being sold in Greenville, SC) and saving it as an XML file to the HDD temporarily to be read with a stream reader. Then, it just displays message boxes one after another showing the title of each post. However, when I run the program, I get the error on this line:
Code:
Dim posts As System.Xml.XmlNodeList = CLdataDoc.SelectNodes("rdf:RDF/item")
"Namespace Manager or XsltContext needed. This query has a prefix, variable, or user-defined function."
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Jun 25, 2009
I'm working with VB.NET 2003 on Windows XP.I'm trying to read in from a text file and populate a listbox with the data. Below is my code:
Code:
If (File.Exists("users.txt")) Then
Dim text As String
FileOpen(1, "users.txt", OpenMode.Output)
Do
text = LineInput(1)
[Code]...
This code never populates the listbox and then on top of that it erases everything in the text file. What am i doing wrong?
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Nov 17, 2010
I am working on a program with multiple collections related to one another for a school project. Each collection needs to have its own defined properties and have the objects written (1 per line) to a text file.
I have all of that working.
When reading the comma-separated line from the file, I want to place one of the properties of the object in a listbox (so that all the objects' names will show up in the listbox). I think I have this part figured out...
My problem is that when you click on the name in the listbox, I would like multiple text boxes to be populated with the appropriate, corresponding properties of the particular object in the collection...is there a way for this to be done?
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May 29, 2009
I want to read the meta data from a movie file and place the result in to a textbox.I've googled it and found no good samples for vb.net =( The data I'm interested in are the bitrate and the resolution and the extensions I'm interested in are .wmv, .avi and .flv the extension isn't known when the program loads because the movie is going to be inputted by the user..
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Feb 5, 2009
I have a coma seperated text file with loads of records. Usually when we read a text file we start from the first line and go towards the last. I know that there will be x comas per record.
But I want to start reading from the last line and then towards the top. This enables me to stop before I reach the top (depending on the data).
What would be the fastest way to read a text file in VB.NET. I am using VS2008. Basically I want to read from last line and stop when I want. I may not need to read the entire file.
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Aug 28, 2010
how to read bytes from a file... but is it possible to read each individual bit, one at a time?
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Jan 31, 2009
I need to read the following file in vb .net:"C:WindowsSoftwareDistributionDataStoreDataStore.edb". It contains info about installed software updates. I've taken a look at the file by opening it with notepad. This isn't a plain-text file obviously, but I can find and see the text I want easily with Notepad, and I want to extract this text by using VB .NET.
The problem is, i've tried to read the file by using an io.streamreader, but I can't get the same results as in notepad. I've tried to change encoding but that doesn't work. I mean in Notepad, I can read some text easily: "A s e c u r i t y i s s u e h a s b e e n i d e n t i f i e d" [...], but the only thing I get with the streamreader is some bunch of ugly characters, and the text I saw with Notepad isn't there.
Do I have to read the file in binary or what? HOW NOTEPAD DOES IT? HOW DO I READ THIS FILE LIKE NOTEPAD DOES?I absolutely need to extract some updates info that aren't in either the registry or WMI/QFE.
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Jul 23, 2010
I got the following code to read an XML file: [Code] Obviously the count limits the amount of lines that it reads. But how do I get it to read all the lines in the file? Ive tried removing the And (count <20) but when I run the program nothing happens.
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Aug 27, 2008
I am writing an application that connects to a specific com port. This com port can change depending on how many physical ports are on the PC, and if other USB devices have installed com ports before this one.
I have the communication to the com port all working great, but I need to get the com port description not just the "COM#" which is all I currently get.
I found in the registry where the description is stored but am having trouble doing what I need.
In this key:
Code:
HKEY_LOCAL_MACHINESYSTEMControlSet001ControlClass{4D36E978-E325-11CE-BFC1-08002BE10318}
there is a varied number of sub keys. The are numbered 0000-NNNN depending on how many ports you have. Inside each of these keys, there are multiple values, although I am only interested in one or 2 of them.
My problem is, that I do not know how to get a list of the subkeys (the 0000-NNNN keys/folders) from the original key I posted. I have looked through a few registry tutorials, and I can view the default value in the listed key, but I could not find how to list the subkeys of the listed key.
Does anyone have any sample code they could share that shows how I can get a listing of subkeys, and then run through those subkeys checking for a specific value in one of the strings contained in the subkey?
I am using VB.net 2008 and Windows XP.
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