VB.NET Accessing C DLL Problems

[webroten]

I've been working through trying to access a C DLL from VB.NET. I've read many online postings, but I'm still having problems. Now, my error is the "Attempted to read or write protected memory" error. Here's my Structure declaration:

[CODE=vbnet]<StructLayout(L ayoutKind.Seque ntial, charset:=CharSe t.Ansi)> _
Public Structure CONFIG_PARM
<MarshalAs(Unma nagedType.LPStr )> Public address1 As String
<MarshalAs(Unma nagedType.LPStr )> Public addrindex As String
<MarshalAs(Unma nagedType.LPStr )> Public cdrom As String
<MarshalAs(Unma nagedType.LPStr )> Public citystate As String
<MarshalAs(Unma nagedType.LPStr )> Public crossref As String
<MarshalAs(Unma nagedType.LPStr )> Public system As String
<MarshalAs(Unma nagedType.LPStr )> Public elot As String
<MarshalAs(Unma nagedType.LPStr )> Public elotindex As String
<MarshalAs(Unma nagedType.LPStr )> Public llkpath As String
<MarshalAs(Unma nagedType.LPStr )> Public ewspath As String
<MarshalAs(Unma nagedType.LPStr )> Public dpvpath As String
<MarshalAs(Unma nagedType.LPStr )> Public fnsnpath As String
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=124) > Public rsvd As String
End Structure

<StructLayout(L ayoutKind.Seque ntial, CharSet:=CharSe t.Ansi)> _
Public Structure Z4OPEN_PARM
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=50)> Public rsvd1 As String
<MarshalAs(Unma nagedType.I4)> Public status As Integer
<MarshalAs(Unma nagedType.LPStr )> Public fname As String
<MarshalAs(Unma nagedType.Struc t)> Public config As CONFIG_PARM
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=1)> Public ewsflag As String
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=1)> Public elotflag As String
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=1)> Public llkflag As String
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=1)> Public dpvflag As String
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=1)> Public systemflag As String
<MarshalAs(Unma nagedType.ByVal TStr, SizeConst:=511) > Public rsvd2 As String
End Structure[/CODE]

The Function declarations and the code used to call them are:

[CODE=vbnet] <DllImport("zip 4_w32.dll", CharSet:=CharSe t.Ansi)> _
Public Shared Function z4opencfgSTD(By Ref openparm As Z4OPEN_PARM) As Integer
End Function

...

Dim openparm As New Z4OPEN_PARM
Dim configparm As New CONFIG_PARM

Dim address1 As String = "e:\ams\ams_com m"
Dim addrindex As String = "e:\ams\ams_com m"
Dim citystate As String = "e:\ams\ams_com m"
Dim crossref As String = "e:\ams\ams_com m"
Dim fnsnpath As String = "e:\ams\ams_com m"
Dim elot As String = "e:\ams\ams_elo t"
Dim elotindex As String = "e:\ams\ams_elo t"
Dim llkpath As String = "e:\ams\lacslin k"
Dim dpvpath As String = "e:\ams\ams_dpv "
Dim systempath As String = "e:\projects\wr apz4\wrapz4\deb ug"
Dim ewspath As String = ""
Dim rsvd_string As New StringBuilder
Dim rsvd As String = ""
rsvd.PadLeft(12 4)
Dim rsvd1 As String = ""
rsvd1.PadLeft(5 0)
Dim rsvd2 As String = ""
rsvd2.PadLeft(5 11)
Dim cdrom As String = ""
Dim fname As String = ""

configparm.addr ess1 = address1
configparm.addr index = addrindex
configparm.cdro m = cdrom
configparm.city state = citystate
configparm.cros sref = crossref
configparm.syst em = systempath
configparm.elot = elot
configparm.elot index = elotindex
configparm.llkp ath = llkpath
configparm.ewsp ath = ewspath
configparm.dpvp ath = dpvpath
configparm.fnsn path = fnsnpath
configparm.rsvd = rsvd

openparm.status = 2
openparm.rsvd1 = rsvd1
openparm.rsvd2 = rsvd2
openparm.elotfl ag = "Y"
openparm.llkfla g = "Y"
openparm.ewsfla g = "N"
openparm.dpvfla g = "Y"
openparm.system flag = "Y"
openparm.fname = fname

openparm.config = configparm

Connection.Text = z4functions.z4o pencfgSTD(openp arm)[/CODE]

Why would I be getting the memory error, "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."?

Thanks for your help.

[Frinavale]

I've been working through trying to access a C DLL from VB.NET. I've read many online postings, but I'm still having problems. Now, my error is the "Attempted to read or write protected memory" error. Here's my Structure declaration:

...

Why would I be getting the memory error, "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."?

Thanks for your help.

I just encountered this type of error today.
What's happening is your C DLL is not properly using the memory allocated to it.

In my case I had to increase the size of the array that I passed to a method because this array was not large enough to hold the data that the function was manipulating. You would think that the developers of the DLL would have managed the memory correctly but this isn't the case.

I haven't really taken a close look at your code that you've posted...but I recommend going through and making sure that any variables declared in your .NET program are allocating enough memory for the C variables....

Especially Strings! C code is notorious for not handling memory allocation for Strings correctly.

(In your case...you may be providing Strings that are too long for the C DLL to handle)

[webroten]

That corrected the problem - thanks! I'm still having problems with the DLL reading my structure, but I don't think it's related to this issue. It could be something else with the marshalling or something.

[Frinavale]

That corrected the problem - thanks! I'm still having problems with the DLL reading my structure, but I don't think it's related to this issue. It could be something else with the marshalling or something.

I'm glad you solved the problem!
If you need help with your other issue start a new post.

Congratz!

-Frinny

[jm1576]

I am working on the same exact project. Were you able to solve your issue ? I have just received the CD from USPS. Could you post the rest of the code that call the other Z4 functions ?

[Frinavale]

I am working on the same exact project. Were you able to solve your issue ? I have just received the CD from USPS. Could you post the rest of the code that call the other Z4 functions ?

Hi Jm1576,

Webroten has only ever posted twice. This user is not very active.
Could you please post your exact error so that we might be able to help you?

-Frinny

[jm1576]

I am using the above code that was posted. This the error that I get

"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

[Frinavale]

I am using the above code that was posted. This the error that I get

"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

This is often a sign that the unmanaged code (the C code) is not using memory correctly. The previous person found that the problem was resolved when they allocated more memory for the C code to use...or else they shortened the strings that they were passing to the C code.

-Frinny

[jm1576]

Hi,
This is what I have changed.
<DllImport("zip 4_w32.dll", CallingConventi on:=CallingConv ention.StdCall, EntryPoint:="z4 opencfgSTD", ExactSpelling:= False), ReliabilityCont ract(Consistenc y.WillNotCorrup tState, Cer.None)> _
Public Shared Function z4opencfgSTD(<[In](), Out()> <MarshalAs(Unma nagedType.LPStr uct)> ByVal parm As Z4OPEN_PARM) As Integer
End Function

This is the error that I am getting now.
"Cannot marshal 'parameter #1': Invalid managed/unmanaged type combination (this value type must be paired with Struct)"