Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

Accessing C++ DLL from C#

Posted on 2007-11-26
11
Medium Priority
?
2,402 Views
Last Modified: 2013-12-16
I'm trying to access functions from a C++ DLL from C#. I neither can reference nor register the dll. Is it possible for me to access the functions within C#?  But it's possible to access the DLL from VB6.


// part of my code is as below:
 
[StructLayout(LayoutKind.Sequential)]
        public struct DataPointValues
        {
            [MarshalAs(UnmanagedType.LPStr, SizeConst = 64)]
            public string pointName;
            [MarshalAs(UnmanagedType.LPStr, SizeConst = 64)]
            public string paramName;
            public int    paramOffset;
            [MarshalAs(UnmanagedType.I2, SizeConst = 1)]
            public int paramType;
            public int paramValue;
        }
 
        [DllImport("hscnetapi.dll", EntryPoint = "rHsc_Param_Value_Put_Bynames")]
        public static extern long rHsc_Param_Value_Put_Bynames(string server, int num_requests, DataPointValues  param_byname_data_array);

Open in new window

0
Comment
Question by:szaranger
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 6
  • 5
11 Comments
 
LVL 96

Expert Comment

by:Bob Learned
ID: 20354399
There is a huge difference between VB6 and VB.NET/C# when it comes to interfacing with C++ DLLs, especially when it comes to string marshalling.  You need to find juse the right combination of attributes.  It would help if you had the C++ prototype declaration to work from.

Bob
0
 
LVL 2

Author Comment

by:szaranger
ID: 20354436
Is it possible to access an unmanaged DLL without regitsering it from C#?
0
 
LVL 96

Expert Comment

by:Bob Learned
ID: 20354464
What kind of DLL are you talking about?  If it is a COM DLL, then it needs to be registered.  Otherwise, you should be able to access it with the right p/invoke signature.

Do you have the signature from the C++ DLL, or is it someone else's DLL?

Bob
0
Prepare for your VMware VCP6-DCV exam.

Josh Coen and Jason Langer have prepared the latest edition of VCP study guide. Both authors have been working in the IT field for more than a decade, and both hold VMware certifications. This 163-page guide covers all 10 of the exam blueprint sections.

 
LVL 2

Author Comment

by:szaranger
ID: 20354486
It is third party COM DLL. The signature is as below:

function rHsc_Param_Value_Puts(Server: LPSTR; num_requests: INT; out param_value_data_array: ^SafeArray): INT; stdcall;
0
 
LVL 96

Expert Comment

by:Bob Learned
ID: 20354531
For 'out' parameters, you need the 'ref' keyword:

...ref DataPointValues  param_byname_data_array

The SafeArray is trickier, and I believe that you might be able to use the VariantWrapper to help out:

VariantWrapper Class:
http://msdn2.microsoft.com/en-us/library/system.runtime.interopservices.variantwrapper(vs.80).aspx

Bob
0
 
LVL 2

Author Comment

by:szaranger
ID: 20354556

When I run the code, it returns me this error:
Unable to find an entry point named 'rHsc_Param_Value_Put_Bynames' in DLL 'hscnetapi.dll'.
[StructLayout(LayoutKind.Sequential)]
        public struct DataPointValues
        {
            [MarshalAs(UnmanagedType.LPStr, SizeConst = 64)]
            public string pointName;
            [MarshalAs(UnmanagedType.LPStr, SizeConst = 64)]
            public string paramName;
            public int    paramOffset;
            [MarshalAs(UnmanagedType.I2, SizeConst = 1)]
            public int paramType;
            public int paramValue;
        }
 
        [DllImport("hscnetapi.dll", EntryPoint = "rHsc_Param_Value_Put_Bynames")]
        public static extern long rHsc_Param_Value_Put_Bynames(string server, int num_requests, ref DataPointValues param_byname_data_array);

Open in new window

0
 
LVL 96

Expert Comment

by:Bob Learned
ID: 20354573
You can use dumpbin (or dependency walker) to view the exports for the DLL to make sure about the entry point name.  It is also possible to use the 'unsafe' keyword and pointers with C# p/invoke signatures.

Example:

Using Unsafe Code in C#
http://www.csharpfriends.com/Articles/getArticle.aspx?articleID=351

Bob
0
 
LVL 2

Author Comment

by:szaranger
ID: 20354625
Dependancy walker returns:
     rhsc_param_value_put_bynames        as the Function and
      A hexadecimal value as a Entry Point
So it is the same name as what I use.


0
 
LVL 2

Author Comment

by:szaranger
ID: 20355445
Apparently .NET cannot access a COM DLL without registering it!!!???
0
 
LVL 96

Accepted Solution

by:
Bob Learned earned 750 total points
ID: 20357690
Hmmm, let's revisit a previous comment:

"If it is a COM DLL, then it needs to be registered".

Bob
0
 
LVL 2

Author Closing Comment

by:szaranger
ID: 31411106
Thanks Bob.
0

Featured Post

Free learning courses: Active Directory Deep Dive

Get a firm grasp on your IT environment when you learn Active Directory best practices with Veeam! Watch all, or choose any amount, of this three-part webinar series to improve your skills. From the basics to virtualization and backup, we got you covered.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
Update (December 2011): Since this article was published, the things have changed for good for Android native developers. The Sequoyah Project (http://www.eclipse.org/sequoyah/) automates most of the tasks discussed in this article. You can even fin…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.

705 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question