Question

I’m writing a wrapper for a dll. The dll has a method whose signature resembles the following:

unsigned long aMethod(char **firstParameter, char **secondParameter))

aMethod returns string pointers to all parameters.

I’ve searching at google for a tutorial to give me insight on how to write the signature on C# so the framework can do the marshalling process.

How can it be written?
Do you know about any tutorial, book or documentation on this subject?

Answer 1

I got the answer:

The signature has to be like this:

[DllImport(aDll.dll, CallingConvention = CallingConvention.Cdecl, 
    CharSet = CharSet.Auto)]
static unsafe extern ulong aMethod(ref IntPtr firstParameter, 
    ref IntPtr secondParameter);

Parameters should be declared as here:

IntPtr firstParameter = new IntPtr();
IntPtr secondParameter = new IntPtr();

And invocation is done as:

aMethod(ref firstParameter, ref secondParameter);

Marshalling and unmarshalling related to the strings as here:

Marshal.PtrToStringAnsi(firstParameter)
Marshal.PtrToStringAnsi(secondParameter)

Obviously, this marshalling has been selected based on dll´s API conventions.

I´m not sure after all, but all the problems had they source in the Charset and CallingConvention options…