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Hey, i am trying to figure out why ReadFile isn't working the way it should in VB.NET. The problem is that I call ReadFile on some file that i open with CreateFile, and it fills a buffer with the first couple of bytes from the file.. that is fine. but when i call ReadFile again, it still returns the same first bytes.. as if it didnt increment the file pointer. Then, i tried checking the file pointer value before and after each call to readfile.. and what seems to happen is that every time readfile is called, the file pointer is reset to 0, because after the first, or second call to readfile the file pointer is correct (the number of bytes i read using the function).. so i guess it gets reset to 0 before it fills the buffer.
here is the code if anyone can help:
<br />
Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Integer, ByVal dwShareMode As Integer, ByRef lpSecurityAttributes As SECURITY_ATTRIBUTES, ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer, ByVal hTemplateFile As Integer) As Integer<br />
<br />
Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Integer) As Integer<br />
<br />
Declare Function ReadFile Lib "kernel32" (ByVal hFile As Integer, ByVal destBuffer() As Byte, ByVal nNumberOfBytesToRead As Integer, ByRef lpNumberOfBytesRead As Integer, ByRef lpOverlapped As OVERLAPPED) As Integer<br />
<br />
...
<br />
<br />
Dim hDisk As Integer<br />
Dim bytesReturned As Integer<br />
<br />
hDisk = CreateFile("E:\somebigfile.dat", _<br />
GENERIC_READ, FILE_SHARE_READ Or FILE_SHARE_WRITE, _<br />
Nothing, OPEN_EXISTING, 0, 0)<br />
<br />
If hDisk = INVALID_HANDLE_VALUE Then Exit Sub<br />
<br />
me.Text = SetFilePointer(hDisk, 0, Nothing, FILE_CURRENT)<br />
<br />
Dim dest() As Byte<br />
ReDim dest(1023)<br />
Dim destLen As Integer = dest.Length<br />
<br />
ReadFile(hDisk, dest, 1024, bytesReturned, Nothing)<br />
PrintData(dest, txt1) 'just a function that writes the data to a textbox txt1<br />
<br />
me.Text &= " " & SetFilePointer(hDisk, 0, Nothing, FILE_CURRENT)<br />
<br />
ReadFile(hDisk, dest, 1024, bytesReturned, Nothing)<br />
PrintData(dest, txt2)<br />
<br />
me.Text &= " " & SetFilePointer(hDisk, 0, Nothing, FILE_CURRENT)<br />
<br />
ReadFile(hDisk, dest, 1024, bytesReturned, Nothing)<br />
PrintData(dest, txt3)<br />
Thank you for any help!!!! This is driving me nuts!!!
r -€
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First, according to the MSDN docs on ReadFile, your buffer should be passed ByRef, not ByVal. Second, are you checking the value of bytesReturned after each read?
Why are you P/Invoking theres functions in the first place? They're wrapped by the System.IO namespace. Using the classes found there is MUCH easier than what your doing. I only say this because your posted code isn't doing anything that these classes couldn't handle.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Well, the buffer is an array, which seems to automatically act as a pointer when it is passed to C functions, also I saw the declaration with ByVal many places and it seemed to work.
I checked bytesReturned after each call, it is 1024. I also tried clearing the array before each call to ReadFile, and it still fills the buffer each time with the first bytes of the file.
I realize now I can use the System.IO namespace and FileStream and such, but this has become more of a curiosity on my part. I am befuddled as to why API functions (I had similar problems calling ZLib DLL functions from VB.NET) don't work properly in VB.NET. Maybe it is something with the managed code heap or something?
Thank you for your reply, however.. if anyone finds anything more on the subject please let me know.
r -€
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 How to set the first parameter of URLDownlofToFIle() in VB.
Private Declare Function URLDownloadToFile Lib "urlmon" _
Alias "URLDownloadToFileA" _
(ByVal pCaller As Long, _
ByVal szURL As String, _
ByVal szFileName As String, _
ByVal dwReserved As Long, _
ByVal lpfnCB As Long) As Long
I have created a dll ,which makes use of the urldownloadtofile win32 API.
This dll works fine from within VB.
But when I access it from ASP ..the urldownloadtofile function ..wont work ..
I supose it has got to do something with the first parameter :
pCaller
Pointer to the controlling IUnknown interface of the calling Microsoft ActiveX component (if the caller is an ActiveX component). If the calling application is not an ActiveX component, this value can be set to NULL. Otherwise, the caller is a Component Object Model (COM) object that is contained in another component (such as an ActiveX control within the context of an HTML page). This parameter represents the outermost IUnknown of the calling component. The function attempts the download within the context of the ActiveX client framework and allows the caller's container to receive callbacks on the progress of the download.
Please help me out...
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ASP/ASP.NET are server side technologies that generate HTML. From with an ASP/ASP.NET Page, the code will run under the account of the web server. This account usually DOES NOT have write permissions to the file system.
If you try and call this function from inside an ActiveX component running in a web page client-side, the same is true. Security restrictions will not allow the component to write to the file system on the client machine.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Hi Dave !
Thanx for ur post.
Anyway ,My dll executes on the web server .Basically what I'm trying to achieve is save an html page on the server and then mail it some recepient ..
i'm in no way trying to save the page on the client m/c ..
thanx n reagrds.
Girija
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Then the ASPNET account that your app is running under doesn't have Write permissions to the folder your trying to save your page to. Go into the Properties/Security tab of whatever folder your saving these pages to and check to see if ASPNET has Write permissions.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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The code you submitted was a pike of commented out code, but I see one glaring problem with your URLDownloadToFile call:
DownloadFile = URLDownloadToFile(x, sSourceUrl, sLocalFile, BINDF_GETNEWESTVERSION, 0&) = ERROR_SUCCESS
The parameter where your passed the constant BINDF_GETNEWESTVERSION is reserved and must always be 0. The new line should read something like this: (NOT TESTED!)
DownloadFile = URLDownloadToFile(0, sSourceUrl, sLocalFile, 0, 0)
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Hi,
I want to dynamically add nodes to treeview control based on database values.
My database structure in MS-Access is as follows (first row is table columns and then follows the data rows):
MyID MyTitle ParentID
1 Root Title 0 'This is the root
2 Title 1 1 '1 indicates it is child to row where MyID=1
3 Title 2 1 '1 indicates it is child to row where MyID=1
4 Title 3 1 '1 indicates it is child to row where MyID=1
5 Title 2.1 2 '2 indicates it is child to row where MyID=2
6 Title 2.2 2
7 Title 3.1 3
8 Title 3.2 3
9 Title 4.1 4
10 Title 4.2 4
11 Title 2.1.1 5
13 Title 2.1.2 5
14 Title 2.1.2.1 11
15 Title 2.1.2.2 11
16 Title 2.1.2.1.1 14
17 Title 2.1.2.1.2 14
18 Title 3.1.1 7
19 Title 3.1.2 7
20 Title 3.1.1.1 18
21 Title 3.1.1.2 18
Any anyone show me how to create this tree? I could reach only upto level 2.
Regards,
Vilas
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I dont have the time to make the complete coding but Ill give you my algorithm idea (I will assume that a parent is alyways before its child in the table):
- create an empty HashTable
- loop through all rows
-- create a TreeNode with the name of MyTitle
-- add the TreeNode to the HashTable with MyID as a key
-- if ParentId is 0
--- then
---- add the TreeNode to the top most Nodes collection of your TreeView
--- else
----look into the HashTable with ParentId as the key
---- cast the result to TreeNode
---- add the current TreeNode to the Nodes collection of the found one
-- endif
- loop end
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Hi,
I want to dynamically add nodes to treeview control based on database values.
My database structure in MS-Access is as follows (first row is table columns and then follows the data rows):
MyID MyTitle ParentID
1 Root Title 0 'This is the root
2 Title 1 1 '1 indicates it is child to row where MyID=1
3 Title 2 1 '1 indicates it is child to row where MyID=1
4 Title 3 1 '1 indicates it is child to row where MyID=1
5 Title 2.1 2 '2 indicates it is child to row where MyID=2
6 Title 2.2 2
7 Title 3.1 3
8 Title 3.2 3
9 Title 4.1 4
10 Title 4.2 4
11 Title 2.1.1 5
13 Title 2.1.2 5
14 Title 2.1.2.1 11
15 Title 2.1.2.2 11
16 Title 2.1.2.1.1 14
17 Title 2.1.2.1.2 14
18 Title 3.1.1 7
19 Title 3.1.2 7
20 Title 3.1.1.1 18
21 Title 3.1.1.2 18
Any anyone show me how to create this tree? I could reach only upto level 2.
Regards,
Vilas
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Hi,
Create a datatable (in database) with the colums 'Code' and 'Upcode' Where de upcode for an rootnode = '-' The upcode for de child nodes is the code from the parent node
The you can use following code
Dim TN as new Treenode
Tn.Tag = "-"
Private Sub Groep_Laad(ByVal Nde As TreeNode, ByVal Isroot As Boolean)
Dim GR As New Ole_DB_Groep()
Dim DT As New DataTable()
Dim Teller As Int16
If Isroot Then
GroepTV.Nodes.Clear()
End If
GR.SelectCommand = "SELECT * FROM TableName WHERE upcode ='" & Nde.Tag & "' ORDER BY Code"
GR.Adaptor.Fill(DT)
With DT
If .Rows.Count > 0 Then
For Teller = 0 To .Rows.Count - 1
Dim NewNode As New TreeNode()
NewNode.Tag = "" & .Rows(Teller).Item("Code")
NewNode.Text = "" & .Rows(Teller).Item("Name")
If Isroot Then
GroepTV.Nodes.Add(NewNode)
Else
Nde.Nodes.Add(NewNode)
End If
Groep_Laad(NewNode, False)
Next
End If
End With
DT.Dispose()
GR.Dispose()
End Sub
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I am using a datgrid in my application. I want to highlight a full row, whenever mouse is moved on the row. Any solution.
Thanks
Sumit Domyan
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You have to handle the MouseMove event and call the HitTest function of the DataGrid with the current mouse position. It will return you an object where you can access the Row at the specified position. With the Select function of the grid you can highlight this row (dont forget to unhighlight the previous row with Unselect).
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Hi,
I have a C-based DLL, that requires callback function. The parameter to this function is a LPCSTR that the C DLL provides on calling.
I have a VB application that implements this callback function & uses the C-Dll. How do I pass parameters for string-handling?
I know I can modify the C-Dll to handle BSTRs instead of LPCSTRs. However, I am looking for an alternative implementation so that I do not have to change the DLL code. Please advise.
Thanks in advance,
Manny
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Hi, I need to write a simple web server, in order to show a web page in a
LAN for 30 users. Could I use VB6.0 or should I use VB.NET?
Thanks
Roberto
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You could use either, but VB.NET will be easier.
BTW: Why write it when there are so many others out there, like Cassini[^].
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Thank you for your reply.
Since I´m building an application, I need to include the web server
to be able to distribute it.
I downloaded the Cassini, but how could i distribute it freely?
Thanks
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Now you've added a wrinkle. Since you now want to distribute someones elses work, you're going to have to contact the authors of ANY web server you download and ask about their licensing requirements.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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When streaming video over the internet, witch way is the best/fastest way to do it?
Send frame by frame?
Send from a avi-stream?
I have a program witch captures frames/video from a webcamera. The picture (bitmap) size is 160*120*24bit
This gives me a buffer size of 57600 bytes (160*120*3) which is too much to data to send.
The upload speed is 256 kilobits/s. which is 32000 bytes/s (256000/8 = 32000)
This give me ~ a half picture/s 
How can I compress this buffer (without the use of 3-party components)?
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You have two choices:
1) Code the compression/decompression on your own (called a "codec") and suffer with nearly zero support from other people.
2) Use codecs that are already written, "industry standard", and supported by others.
The choice is up to you. If it were me, I'd skip writing my own codec...
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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I agree... but: should the stream be frame by frame or avi stream???
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That's not as straight forward as it would seem. There are many methods for compressing a video stream into a data stream and sending it. It sould like your talking about both using the same terms. AVI is just a compressed video stream format.
You can compress the video stream using either a full frame compression technique, or partial frames with key frames, or several frames at once. There are dozens of different techniques that fall under each of these categories.
Sending the data can be done over TCP, UDP, or Multicast IP. The choice is up to you.
But unless you writing code to explore these techniques and come up with your own format, you'd be MUCH better off using third party components that follow industry standards for video compression and transmission. The Microsoft Windows Media SDK[^] would be a good place to start.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Hi,
I need to dynamically add table rows and text boxes. When the user clicks "add" , on postback i am adding new and textboxes.
The problem is the page moves up and the newly added textboxes are out of sight. the user has to scroll down and find where the new row is added. I have different sections to which new rows can be added.
Any clues how I can find the position of the newly added textbox and move the page up to that location. I am using vb.net
thanks,
Soujanya
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Hi! I really need some's help who has extensive experience working with FileSystemWatcher object in vb.net. I've a production application I've written that monitors local and network files for creation/changes. My problem is that the FSW seems to be very inconsistent in picking up files. I've done extensive research and tried several methods, but overall I still have problems getting it work my way. I only monitor a handfull (10-12) files so it's not an overload of events issue. I know many of you would want to have more details before attempting to help, but I'd rather if someone who's willing to spend a bit of time to review my code in general and give me a suggestion or 2 would contact me. Any help is appreciated. I'm including the basic logic of what my application is trying to do below:
1) Service runs every 30 minutes
2) checks database for any records for files to watch
3) locates those records, creates 1 FSW object for each record with
File Name and Path pointing to the info in database, wires up OnChanged,
OnRenamed, OnCreated, and OnDeleted events to their handlers
4) Adds the instance of the FSW object to global shared Hashtable
5) Updates SQL status for this file to 2, meaning that FSW created, waiting
for the file to be generated/updated.
6) OnChanged event contains the code that reacts on 2 types of events
OnChanged and OnCreated. When it fires, it checks that the instance of FSW
that raised the event is contained in global hashtable. If so, it connects to
database and gets the XML options for this specific file (such as FTP file,
email it, back it up, etc...)
7) In OnChanged event there's loop inside of which it keeps trying to rename
the file that has raised the event to a new name (just appends one to the
end of the file name). This is done so that if the file is very large it would not
try to work with it (FTP or something else) until it's fully written.
Once it's able to rename it, it means the system no longer has a lock on the
file. It then renames the file to its original name and kicks off the
function that process the XML actions associated with this file.
8) Upon completion of all the actions or in case of failure the SQL status
for this file is updated (1 for success, 3 for failure.
9) The reference for this FSW object is removed from global hashtable.
10) Same thing is done for any other files that have been picked up by the service
when it ran initially with same logic.
11) Service runs once again in 30 minutes.
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