Marshalling char** from C DLL to C#

[Ricardo Nunnini]

I have a function in a DLL that returns a char**.

What is the correct MarshalAs attribute incantation to use? I've tried just
about every combination I can think of, the best seems to be [MarshalAs(UnmanagedType.LPArray,
ArraySubType=UnmanagedType.LPStr, SizeParamIndex=1)] but even that just keeps
returning a (char**)null.

All ideas gratefully received...

[Mattias Sjögren]

Ricardo,

>What is the correct MarshalAs attribute incantation to use?

I suggest you type the parameter as "out int", and then pass the
pointer you get back to Marshal.PtrToStringAnsi() to retrieve the
actual string. In beta 2, you'll use IntPtr instead of int.


Mattias

====================================
Mattias Sjögren - mattias @ mvps.org
http://www.msjogren.net/dotnet/

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[Ricardo Nunnini]

Mattias

Yipes! I thought we weren't meant to do naughty things like that anymore
in the .NET world. I'll do it if it works, but I *know* I'll feel guilty
afterwards

I can see that Marshal.PtrToStringAnsi() would give me a nice Ansi string
from a pointer, but how about my array of strings (the function in the DLL
returns a char**, not just a char*)? Is there some magic with Marshal.AddOfArrayElement(arr,index)?

Ricardo

PS Thanks for the fast, and helpful, response.

[Eric Gunnerson]

Note that you also have to worry about who's going to free the returned
object (if it needs to be freed).

You could consider the managed extensions to C++; they provide much more
control.

"Mattias Sjögren" <mattias.dont.want.spam@mvps.org> wrote in message
news:3af3fd3f.625709@news.devx.com...
> Ricardo,
>
> >What is the correct MarshalAs attribute incantation to use?
>
> I suggest you type the parameter as "out int", and then pass the
> pointer you get back to Marshal.PtrToStringAnsi() to retrieve the
> actual string. In beta 2, you'll use IntPtr instead of int.
>
>
> Mattias
>
> ====================================
> Mattias Sjögren - mattias @ mvps.org
> http://www.msjogren.net/dotnet/
>
> CodeHound - The Software Developer's Search Engine
> http://www.codehound.com