string conversion

[smokljan]

Hello everyone,

I'am a C# programmer, but I have problem with code in c++. Code in c++ (it is unamanaged provider for EBS for Sharepoint, if anyone is interested) calls c# function which is supposed to return string (actually, path of a file on disk), and in c++ that string should be converted in LPCTSTR. Which is the correct way of doing this, what type should be returned from c# to c++ and which type should be receieving type in c++ (I've tried std::string and LPWSTR, not working), and how to convert it then to LPCTSTR?

Here is the code that I've tried so far, and not working:
c++;

HRESULT hr = CoInitialize(NULL);
// Make a smart pointer to the IGetPathClass interface in DLL
IGetPathClassPtr pIGetPathClass(__uuidof(CGetPathClass));   
// Return path using the ADD API

LPWSTR result;

hr = pIGetPathClass->GetPath(SiteID, FileID, &result);
// Release the COM interface
CoUninitialize();
		
wstring tTempStr; 
tTempStr.assign(result.begin(), result.end()); 
LPCTSTR tPath = tTempStr.c_str();

c# (just returns string):

public interface IGetPathClass
    {
       string GetPath(Guid a, Guid b);
    }
    public class CGetPathClass : IGetPathClass
    {
        public string GetPath(Guid a, Guid b)
        {            
            return "c:\\temp\\aaa";         
        }
    }

[Computergeek01]

I'm not sure how things are done in C# but in c++ when you declare that a member function takes two variables and returns a string it doesn't work to pass it three variables and cast the string that it returns to an HRESULT.

[smokljan]

I worked by this example:

http://cppkid.wordpress.com/2009/01/02/how-to-call-a-managed-dll-from-unmanaged-code/

This is exactly what I need, just with "string" type instead of "long" type.

[Computergeek01]

Take that tutorial and kill it with fire. I had to take a break from reading it after they referred to a function as an API, I couldn't even begin to understand the half assed hackish approach they are taking to accomplish a simple task like adding a custom class into a DLL. You will learn nothing useful from that site.

It's easy take line 8 in your code, append it to line 12 then delete "hr" and ", &result". Now tTempStr holds the string returned from your function. If your still having trouble copy paste your new code along with the error youre getting.

EDIT: I did a little more reading, just one more paragraph and I want to say there is no reason to register the dll, none what so ever.

[smokljan]

It was strange for me also to see that kind of function call. That article originated from Microsoft, and they say that is is the right function call.

http://support.microsoft.com/kb/828736

When I move line 8 to 12 and delete what you've said, I get an error "function does not take two arguments".

[Computergeek01]

It must be something to do with .Net then. I looked at the M$ article and I'd agree with you that this is the way they want you to call it but I can't make heads or tails of the " logic".