LPCSTR marshalling to unmanaged dll

  • Thread starter Thread starter John Lucas
  • Start date Start date
J

John Lucas

I wish to call an unmanaged function from vb delacred as so:

#define DllExport __declspec(dllexport)
DllExport int WINAPI DllAlcWrite(HANDLE, LPCSTR, int);


I have tried:

1.)
Private Declare Ansi Function DllAlcWrite Lib "alcsapi" (ByVal hConn
As Long, ByVal strGWOutgoing As String, ByVal intStringLength As
Integer) As Integer

<VBFixedString(255)> Private strOutgoingBuffer As String
strOutgoingBuffer ="FOO"
intReturn = DllAlcWrite(m_Handle, strOutgoingBuffer, 3)

2.)
<DllImport("alcsapi.dll")> _
Private Shared Function DllAlcWrite(ByVal hConn As Long, ByVal
strGWOutgoing As String, ByVal intStringLength As Integer) As Integer
End Function
<VBFixedString(255)> Private strOutgoingBuffer As String
strOutgoingBuffer ="FOO"
intReturn = DllAlcWrite(m_Handle, strOutgoingBuffer, 3)

3.)
<DllImport("alcsapi.dll", CharSet:=CharSet.Ansi,
CallingConvention:=CallingConvention.Cdecl)> _
Private Shared Function DllAlcWrite(ByVal hConn As Long, ByVal
strGWOutgoing As String, ByVal intStringLength As Integer) As Integer
End Function
<VBFixedString(255)> Private strOutgoingBuffer As String
strOutgoingBuffer ="FOO"
intReturn = DllAlcWrite(m_Handle, strOutgoingBuffer, 3)

( i know the handle is long, but it is working for other functions in
this dll)

I have also tried setting the string length (3rd parm)to 255
I am able to call other functions in this dll ok
=================================

All of them generate the NullReference exception. Is there a way to
properly marshal LPCSTR?

Help!
 
( i know the handle is long, but it is working for other functions in
this dll)
Click to expand...

Did you mean to say that it isn't a Long? Because it isn't, and you
should replace it with IntPtr or Integer.



Mattias
 
Mattias,

It doesn't seem to matter, I still get a nullreference exception with
this:

<DllImport("alcsapi.dll", CharSet:=CharSet.Ansi,
CallingConvention:=CallingConvention.Cdecl)> _
Private Shared Function DllAlcWrite(ByVal hConn As Long, ByVal
strGWOutgoing As String, ByVal intStringLength As Integer) As Integer
End Function
<DllImport("alcsapi.dll")> _
Private Shared Function DllInitAlc(ByVal Board As Integer, ByVal
lngLine As Integer, _
ByVal GWName As String, ByVal IA As Integer, ByVal TA As Integer) As
IntPtr
End Function

Dim m_handle as IntPtr
m_Handle=DllInitAlc(CInt(lngBoard), CInt(lngLine), strServer,
lngIAHex, lngTAHex)
'(got a non zero handle)


<VBFixedString(255)> Private strOutgoingBuffer As String
strOutgoingBuffer ="FOO"

intReturn = DllAlcWrite(m_Handle, strOutgoingBuffer, 3)
'(exception)
 
John,
<DllImport("alcsapi.dll", CharSet:=CharSet.Ansi,
CallingConvention:=CallingConvention.Cdecl)> _
Private Shared Function DllAlcWrite(ByVal hConn As Long, ByVal
strGWOutgoing As String, ByVal intStringLength As Integer) As Integer
End Function
Click to expand...

Did you change anything? hConn is still declared as Long.



Mattias
 
I wish to call an unmanaged function from vb delacred as so:

#define DllExport __declspec(dllexport)
DllExport int WINAPI DllAlcWrite(HANDLE, LPCSTR, int);


I have tried:

1.)
Private Declare Ansi Function DllAlcWrite Lib "alcsapi" (ByVal hConn
As Long, ByVal strGWOutgoing As String, ByVal intStringLength As
Integer) As Integer
Click to expand...


Private Declare Ansi Function DllAlcWrite Lib "alcsapi.dll" _
(ByVal hConn As IntPtr, _
ByVal strGWOutgoing As String, _
ByVal intStringLength As Integer) As Integer

' air code :)
Dim buffer As String = new String(vbNullChar, 255)
DllAlcWrite (hConn, buffer, buffer.Length)

HTH
 
Tom,

That was it! Null termination character.

Here's what I ended up with.

Dim buffer As String
buffer = strSendThis
buffer.PadRight(255, vbNullChar)
intReturn = DllAlcWrite(m_SabreHandle, buffer, buffer.Length)


THANK YOU.
-john
 
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