Unmanaged DLL in C# Web Service
- by Telis
Hi Guys, please help µe as I am new into accessing an unmanaged DLL from C#..
I have a large unmanaged DLL in C++ and I am trying to access the DLL's classes and functions from a C# Web Service.
I have seen many examples how to use DLLImport, but for some reason I am stuck with my very first wrapper method spending many hours with no luck.. What should I do to return an object in my 'Marshaled' [DllImport..] function? I would like to do something like that:
[DllImport("unmanaged.dll")]
public static extern MyClass MyFunction();
Here is the definition of my C++ class and the function that I want to access:
class __declspec(dllexport) TPDate
{
public:
TPDate();
TPDate(const TPDate& rhs);
...
//today's date.
static TPDate AsOfDate(void);
...
}
In my Web service I have declared the following StructLayout:
[StructLayout(LayoutKind.Sequential)]
public class TPDate
{
public TPDate(TPDate d)
{
_tpDate = d;
}
public TPDate _tpDate;
}
and here's where I think that I'm not doing something right:
class WrapperTPDate
{
[DllImport("TPTools.dll",
ExactSpelling=false,
EntryPoint = "?AsOfDate@TPDate@@SA?AV1@XZ",
CallingConvention = CallingConvention.StdCall)]
[return: MarshalAs(UnmanagedType.Struct)]
**public static extern TPDate AsOfDate();**// HERE THERE IS PROBLEM
};
I am calling the wrapper as follows from my WebMethod:
[WebMethod]
public void ConstructModel()
{
TPDate date1 = WrapperTPDate.AsOfDate();// Here I get exception
TPDate date = new TPDate(date1);
}
The exception i am getting is:
System.Web.Services.Protocols.SoapException: Server was unable to process request. --->
System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal 'return value':
Invalid managed/unmanaged type combination (this type must be paired with LPStruct or
Interface).
If I change it to LPSTRUCT, I am getting another exception:
System.Web.Services.Protocols.SoapException: Server was unable to process request. --->
System.AccessViolationException: Attempted to read or write protected memory. This is often an
indication that other memory is corrupt
Could you please tell me where I'm doing wrong here
Thanks
