How to convert some C++ method to C# call?

Question

I have a C++ dll that contains this method in the header (C++ code):

   enum Error
   {
          Error1,
          Error2,
          Error3,
   }

   void foo(const char* str, Error &err) ;

I am trying to call this method using a DllImport attribute but with no success. All other methods on this dll I can call with no problem.

On the DllImport I converted foo method to this:

   enum Error
   {
          Error1,
          Error2,
          Error3,
   }

   [DllImport("dll_name.dll")]
   public static extern void foo(string str, ref Error err);

but this isn't working either. I've also tried to use 'MarshalAs(UnmanagedType.LPStruct)' on the string and tried to change the 'CharSet' on the dllImport attribute => but nothing works

What does "no success" mean? An error message? Invalid results? — D Stanley, Mar 10 '15 at 20:04
Exception ... no ability to call this method ... but from C++ code i can call this method with no problem — Yanshof, Mar 10 '15 at 20:04
What exception do you get? And what does `foo` do? Does it try to modify the string that's passed in? — D Stanley, Mar 10 '15 at 20:06
Take a look at [how to marshall char*](http://stackoverflow.com/questions/162897/marshal-char-in-c-sharp). You might want to use LPCTSTR instead of const char*. — bokibeg, Mar 10 '15 at 20:07
the string is const ... can't change it .. i don't know what foo do internal. — Yanshof, Mar 10 '15 at 20:07
bokibeg ... please read the question. i already try to change the CharSet — Yanshof, Mar 10 '15 at 20:09
Could the problem be in the 2nd parameter? Perhaps just make it a uint to see if it works: "public static extern foo(string str, ref uint err);" — David Ching, Mar 10 '15 at 22:00
Are you sure the 'foo' function is visible externally? Can you see it in a tool like 'depends.exe'? [http://www.dependencywalker.com/] — karmasponge, Mar 10 '15 at 22:06
@Yanshof are you sure that the issue lies in the string paramater — David Watts, Mar 10 '15 at 22:19
What is the exact exception message? "no ability to call this method" is not it. — David Ching, Mar 10 '15 at 22:21

Ryan McCurry · Answer 1 · 2015-03-10T22:33:07.633

0

I would try this, I notice the lack of the void.

enum Error
{
      Error1,
      Error2,
      Error3,
}

[DllImport("dll_name.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern void foo([MarshalAs(UnmanagedType.LPStr)] string str, ref Error err);

I would also make sure the method is visible in your application. Noted by karmasponge

EDIT: You can try changing calling convention. If the exception you get is a StackImbalance, this should fix the issue.

edited Mar 10 '15 at 22:33

answered Mar 10 '15 at 22:04

Ryan McCurry

1
3

try already ... nothing work. the method is visible - this is not problem if visibility – Yanshof Mar 10 '15 at 22:11

How to convert some C++ method to C# call?

1 Answers1