Using a legacy DLL file in a C# project

Doodlebug

Hi, I'm trying to use a legacy dll file in a Visual C# project.

This is how the code was provided for use in a C++ environment:

[DllImport("OldDll.dll")]
public static extern uint DLL_SaveInfo(void * objptr, Char* filename);

... it is called later as:

DLL_SaveInfo(instance, "C:\\Logfile.txt")))

Of course, C# is not happy with "Char*", so I am not sure of the correct way to use this in C#.

I have tried replacing Char* with String - and it will compile, but the data is not put in the path specified (not sure where in memory it ends up?!).

I have also tried using a variable instead of a String Literal as the path, but this has the same result.

I don't have access to the source of the DLL.

Is there another method of getting this to work in C# that I am missing?

Any help is appreciated!

AlmightyCushion

You use string for const char*. For char* stringbuilder should work.

fasty

Something like this?

[DllImport("OldDll.dll")]
public static extern uint DLL_SaveInfo(IntPtr objptr, [MarshalAs(UnmanagedType.LPStr)] string filename);

The alternative is to write a C++/CLI wrapper DLL that can call the native DLL functions without any P/Invoke stuff.

So: C# App <-- Wrapper DLL --> Native DLL

I prefer P/Invoke personally, but it can take a few shots to get the param marshalling right.

Regarding using Stringbuilder. That's only required for out parameters.

Doodlebug

Thanks for the replies - I will post an update when I get a solution up and running - still getting my head around this! I'm learning that I have a lot more to learn!