DllImport C ++ DLL to C # application, BYTE * p
I have an exported function in a C ++ DLL.
// C++ DLL (Blarggg.dll)
extern "C"
{
USHORT ReadProperty( BYTE * messsage, USHORT length, BYTE * invokeID )
{
if( invokeID != NULL ) {
* invokeID = 10 ;
}
return 0;
}
}
What I would like to make available for my C # application
// C# app
[DllImport("Blarggg.dll")]
public static extern System.UInt16 ReadProperty(
/* [OUT] */ System.Byte[] message,
/* [IN] */ System.UInt16 length,
/* [OUT] */ System.Byte[] invokeID );
private void DoIt()
{
System.Byte[] message = new System.Byte[2000];
System.Byte[] InvokeID = new System.Byte[1];
System.UInt16 ret = ReadProperty( message, 2000, InvokeID ); // Error
}
The problem is I keep getting the following error message.
Blarggg.dll received an uncaught exception of type "System.NullReferenceException" Additional Information: An object reference is not set on an object instance.
I am using VS2008 to build DLL and C #.
I am not a C # programmer.
What am I doing wrong?
I pasted your code straight into VS2008 and it works fine on my 32 bit machine (added .def file to set the exported name). Is your C ++ library a pure win32 project? The error message you provided seems to imply that it raised a CLR exception.
Try the following:
[DllImport("Blarggg.dll", CallingConvention := CallingConvention.Cdecl)]
public static extern System.UInt16 ReadProperty(
/* [IN] */ System.Byte[] message,
/* [IN] */ System.UInt16 length,
/* [OUT] */ out System.Byte invokeID );
private void DoIt()
{
System.Byte[] message = new System.Byte[2000];
System.Byte InvokeID;
System.UInt16 ret = ReadProperty( message, 2000, out InvokeID );
}
You may need to use the System.Runtime.InteropServices.Marshal class to convert between managed and unmanaged types.
Can you do this with C ++ types?
I was under the impression that you can use the DLLImport C DLLs.
We use DLLImport with C ++ Dll just fine, but we declare our external functions as
extern "C" __declspec(dllexport) ...
Take a look at this web page:
http://dotnetperls.com/dllimport-interop