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Call an C++ function from VB.NET
I'm trying to use an unmanaged C++ DLL in my VB.NET application, except that I get a NullReferenceException when calling some of the DLL functions.
The source code for the DLL: http://www.fileuniverse.com/tak/utils/HPI%20Util%20v21.zip (This also contains a VB6 example, but I'm using VB.NET)
The source code for my application (the part that interacts with the DLL) is located in the Code snippet that is attached. I can use the Open and Close function calls fine in my HPIController class, but when I try to use GetFileList I get a NullReferenceException on the HPIDir call. I presume that VB.NET isn't passing the variables correctly, or I'm not meant to use String to pass strings to the DLL.
Exact error message:
An unhandled exception of type 'System.NullReferenceExcep
Additional information: Object reference not set to an instance of an object.
What do I need to do to call the function correctly?
The source code for the DLL: http://www.fileuniverse.com/tak/utils/HPI%20Util%20v21.zip (This also contains a VB6 example, but I'm using VB.NET)
The source code for my application (the part that interacts with the DLL) is located in the Code snippet that is attached. I can use the Open and Close function calls fine in my HPIController class, but when I try to use GetFileList I get a NullReferenceException on the HPIDir call. I presume that VB.NET isn't passing the variables correctly, or I'm not meant to use String to pass strings to the DLL.
Exact error message:
An unhandled exception of type 'System.NullReferenceExcep
Additional information: Object reference not set to an instance of an object.
What do I need to do to call the function correctly?
'''''''''''''''''''''''''' START HPIUtil.vb ''''''''''''''''''''''''
Option Explicit On
Module HPIUtil
Public Const NO_COMPRESSION = 0
Public Const LZ77_COMPRESSION = 1
Public Const ZLIB_COMPRESSION = 2
Public Const TAK_COMPRESSION = 3
Public Const TAK_NOCOMPRESSION = 4
'
' Used to accept string values passed to the callback routine.
Public Structure CString
Dim Data() As Byte
End Structure
'
' GetTADirectory - Returns the directory that TA is installed in
' Arguments:
' DirName - String variable to hold the returned directory
'
Declare Sub GetTADirectory Lib "HPIUTIL.DLL" (ByVal DirName As String)
'
' GetTAKDirectory - Returns the directory that TAK is installed in
' Arguments:
' DirName - String variable to hold the returned directory
'
Declare Sub GetTAKDirectory Lib "HPIUTIL.DLL" (ByVal DirName As String)
'
' HPIOpen - Opens an HPI archive
' Arguments:
' FileName - The name of the HPI file
' Returns:
' If not successful, returns 0
' Either the file does not exist, or it's not a valid
' HPI file
' Otherwise, return a handle to the HPI file that is
' used in the other functions
'
' When finished, use HPIClose to close the archive
'
Declare Function HPIOpen Lib "HPIUTIL.DLL" (ByVal FileName As String) As Long
'
' HPIGetFiles - Enumerate all of the files in the HPI archive
' Arguments:
' HPI - handle to open HPI file returned by HPIOpen
' NextEntry - Set to 0 if this is the start of the search.
' Oterwise, set to the return value of the last
' HPIGetFiles call
' Name - String variable to hold the returned file name
' The name includes the complete path of the file in
' the HPI archive.
' FileType - Long variable to hold the file type
' 0 = File, 1 = Directory
' Size - Long variable to hold the file size
' If the file is a directory, this is the number
' of files in the directory.
' Otherwise, it is the uncompressed size of the file.
' Returns:
' Returns 0 if there are no more files to enumerate.
' Otherwise, returns a value to use as the 'NextEntry' argument
' for the next call to HPIGetFiles.
' Name, FileType, and Size are set to the appropriate values.
'
Declare Function HPIGetFiles Lib "HPIUTIL.DLL" (ByVal HPI As Long, ByVal NextEntry As Long, ByVal Name As String, ByVal FileType As Long, ByVal Size As Long) As Long
'
' HPIDir - Enumerate all of the files in a subdirectory in the HPI archive
' Arguments:
' HPI - handle to open HPI file returned by HPIOpen
' NextEntry - Set to 0 if this is the start of the search.
' Oterwise, set to the return value of the last
' HPIDir call
' DirName - The directory name whose files you want to list
' Name - String variable to hold the returned file name
' The name does not include any path information.
' FileType - Long variable to hold the file type
' 0 = File, 1 = Directory
' Size - Long variable to hold the file size
' If the file is a directory, this is the number
' of files in the directory.
' Otherwise, it is the uncompressed size of the file.
' Returns:
' Returns 0 if there are no more files to enumerate.
' Otherwise, returns a value to use as the 'NextEntry' argument
' for the next call to HPIDir.
' Name, FileType, and Size are set to the appropriate values.
'
Declare Function HPIDir Lib "HPIUTIL.DLL" (ByVal HPI As Long, ByVal NextEntry As Long, ByVal DirName As String, ByVal Name As String, ByVal FileType As Long, ByVal Size As Long) As Long
'
' HPIClose - Close an open HPI archive
' Arguments:
' HPI - handle to open HPI file returned by HPIOpen
' Returns:
' Always returns 0
'
' Always close the archive with HPIClose.
'
Declare Function HPIClose Lib "HPIUTIL.DLL" (ByVal HPI As Long) As Long
'
' HPIOpenFile - Decode a file inside an HPI archive to memory
' Arguments:
' HPI - handle to open HPI file returned by HPIOpen
' FileName - Fully qualified file name to open
' Returns:
' 0 if not successful
' else returns pointer to memory block holding entire file.
' Note: This can be a big chunk of memory, especially for large maps.
' When finished, use HPICloseFile to deallocate the memory
'
Declare Function HPIOpenFile Lib "HPIUTIL.DLL" (ByVal HPI As Long, ByVal FileName As String) As Long
'
' HPIGet - Extract data from file extracted by HPIOpenFile
' Arguments:
' Dest - Destination address
' FileHandle - Pointer returned by HPIOpenFile
' offset - offset within FileHandle
' bytecount - number of bytes to copy
'
Declare Sub HPIGet Lib "HPIUTIL.DLL" (ByVal Dest As Long, ByVal FileHandle As Long, ByVal offset As Long, ByVal ByteCount As Long)
'
' HPICloseFile - Closes a file opened with HPIOpenFile
' Arguments:
' FileHandle - pointer previously returned by HPIOpenFile
' Returns:
' Always returns 0
'
Declare Function HPICloseFile Lib "HPIUTIL.DLL" (ByVal FileHandle As Long) As Long
'
' HPIExtractFile - Extract a file from an HPI file to disk
' Arguments:
' HPI - handle to open HPI file returned by HPIOpen
' FileName - Fully qualified file name to extract
' ExtractName - File name to extract it to
' Returns:
' 0 if not successful
' non-zero if successful
'
Declare Function HPIExtractFile Lib "HPIUTIL.DLL" (ByVal HPI As Long, ByVal FileName As String, ByVal ExtractName As String) As Long
'
' HPICreate - Create an HPI archive
' Arguments:
' FileName - The name of the HPI file to create
' Callback - The address of a callback function (see notes)
' If there is no callback function, use 0
' Returns:
' 0 if not successful
' else returns handle to be used in
' HPICreateDirectory, HPIAddFile, and/or HPIPackFile
' Note:
' Any existing HPI archive with this name will be overwritten.
'
' This function prepares a new HPI archive. After this, call
' HPIAddFile and/or HPICreateDirectory for each file you want to add.
' When all files have been added, call HPIPackFile to actually create
' the HPI archive.
'
' The callback function is called periodically during the pack process
' so that the program can display progress information.
' It's defined thusly:
' Function HPICallBack(ByVal FileName As CString, ByVal HPIName As CString, FileCount As Long, FileCountTotal As Long, FileBytes As Long, FileBytesTotal As Long, TotalBytes As Long, TotalBytesTotal As Long) as Long
' Arguments:
' FileName - the file name being packed.
' HPIName - the name in the HPI file that it's being packed into
' FileCount - the number of the file being packed
' FileCountTotal - the total number of files to pack
' (use these to display 'File 1 of 20' type messages)
' FileBytes - The amount of the file that has been packed
' FileBytesTotal - The file size to be packed
' TotalBytes - The total amount of data that's been packed
' TotalBytesTotal - The total amount of data to be packed
' Return value:
' Return non-zero to stop the pack process
' return 0 to continue the pack process
'
' IMPORTANT NOTE: For TAK compression, this callback function is called
' between 2 files compression (not during compression of a file).
' So, follow are the changements:
' FileBytes : It's the compressed size of current file
' FileBytesTotal : It's the uncompressed size of current file
' TotalBytes: It's the compressed size of ALL files packed
' TotalBytesTotal : It's the uncompressed size of ALL files packed
'
'
' If you don't want to use a callback function, pass 'vbNullString' as
' the Callback argument.
'
' More notes:
' The FileName and HPIName arguments are C-style NULL-terminated strings.
' VB has problems interpreting these, as its internal string format is
' different. If you need to access these values, use the included
' MakeVBString function to convert them to VB-style strings.
'
Public Delegate Sub CallbackFunction(ByVal FileName As CString, ByVal HPIName As CString, ByVal FileCount As Long, ByVal FileCountTotal As Long, ByVal FileBytes As Long, ByVal FileBytesTotal As Long, ByVal TotalBytes As Long, ByVal TotalBytesTotal As Long)
Declare Function HPICreate Lib "HPIUTIL.DLL" (ByVal FileName As String, ByVal Callback As CallbackFunction) As Long
'
' HPICreateDirectory - Create a directory in an HPI archive
' Arguments:
' Pack - the handle returned by HPICreate
' DirName - the complete directory name to create
' Returns:
' 0 if not successful
' non-zero if successful
' Note:
' This function is the only way to create an empty supdirectory in the
' HPI archive.
'
Declare Function HPICreateDirectory Lib "HPIUTIL.DLL" (ByVal Pack As Long, ByVal DirName As String) As Long
'
' HPIAddFile - Add a file to an HPI archive
' Arguments:
' Pack - the handle returned by HPICreate
' HPIName - the complete path and file name to create in the HPI archive
' FileName - the file name on disk to add
' Returns:
' 0 if not successful
' non-zero if successful
' Note:
' Directories in the HPI archive will be created as necessary.
'
Declare Function HPIAddFile Lib "HPIUTIL.DLL" (ByVal Pack As Long, ByVal HPIName As String, ByVal FileName As String) As Long
'
' HPIAddFileFromMemory - Add a file in memory to an HPI archive
' Arguments:
' Pack - the handle returned by HPICreate
' HPIName - the complete path and file name to create in the HPI archive
' FileBlock - pointer to file in memory to add
' FSize - length of FileBlock
' Returns:
' 0 if not successful
' non-zero if successful
' Note:
' Directories in the HPI archive will be created as necessary.
'
Declare Function HPIAddFileFromMemory Lib "HPIUTIL.DLL" (ByVal Pack As Long, ByVal HPIName As String, ByVal FileBlock As Long, ByVal FSize As Long) As Long
'
' HPIPackArchive - Pack the HPI archive
' Arguments:
' Pack - the handle returned by HPICreate
' CMethod - One of LZ77_COMPRESSION or ZLIB_COMPRESSION
' Returns:
' 0 if not successful
' non-zero if successful
' Note:
' The 'Pack' handle is no longer valid after this call.
' The Callback function specified in the HPICreate function is called
' periodically during the pack process.
' This function will not return until the packing is complete, which can
' take awhile for large amounts of data.
'
Declare Function HPIPackArchive Lib "HPIUTIL.DLL" (ByVal Pack As Long, ByVal CMethod As Long) As Long
'
' This is here so that older programs that use this function won't break.
' Use HPIPackArchive(Pack, LZ77_COMPRESSION) instead
'
Declare Function HPIPackFile Lib "HPIUTIL.DLL" (ByVal Pack As Long) As Long
Function MakeVBString(ByVal X As CString) As String
'
' Converts a C-style null-terminated string to a VB-style string
'
Dim I As Integer
Dim Result As String
Result = ""
I = 0
While X.Data(I) <> 0
Result = Result + Chr(X.Data(I))
I = I + 1
End While
MakeVBString = Result
End Function
Function StripNull(ByVal TStr As String) As String
Dim X As Integer
Dim XStr As String
X = InStr(TStr, Chr(0))
If X <> 0 Then
XStr = Left$(TStr, X - 1)
Else
XStr = RTrim$(TStr)
End If
StripNull = XStr
End Function
End Module
'''''''''''''''''''''''''' START HPIController.vb ''''''''''''''''''''''''
Public Structure fileU
Public fileName As String
Public fileSize As Long
Public isDir As Boolean
End Structure
Public Class HPIController
Private HPI_ID As Long
Private HPI_Open As Boolean
Public Function Open(ByVal FileName As String) As Boolean
If (HPI_Open = False) Then
HPI_ID = HPIOpen(FileName)
If (HPI_ID = 0) Then
HPI_Open = False
Return False
Else
HPI_Open = True
Return True
End If
Else
Return False
End If
End Function
Public Function Close()
HPIClose(HPI_ID)
HPI_Open = False
End Function
Public Function GetFileList(ByVal dir As String) As ArrayList
' Gets a list of files that are in the archive
Dim files As ArrayList
Dim fileName As String = Space(255)
Dim fileSize As Long = 0
Dim fileType As Long = 0
Dim nextEntry As Long = 0
Dim directory As String = dir
nextEntry = HPIDir(HPI_ID, nextEntry, directory, fileName, fileType, fileSize)
Dim f As fileU
f.fileName = fileName
f.fileSize = fileSize
f.isDir = (fileType = 1)
files.Add(f)
While (Not nextEntry = 0)
nextEntry = HPIDir(HPI_ID, nextEntry, directory, fileName, fileType, fileSize)
Dim f2 As fileU
f2.fileName = fileName
f2.fileSize = fileSize
f2.isDir = (fileType = 1)
files.Add(f2)
End While
Return files
End Function
Public Function ExtractFile(ByVal fileName As String, ByVal extFile As String) As Boolean
' Gets a list of files that are in the archive
Return (Not HPIExtractFile(HPI_ID, fileName, extFile) = 0)
End Function
End Class
C++Visual Basic.NET
Last Comment
hach-que