How marshalling return array of string on C#

Question

I have below function on C++ (header)

string               __declspec(dllexport) *GetReaders(int& readerCount);

I wrote below method on C# for invoking

[DllImport("ABC.dll", CharSet = CharSet.Auto )]
        extern static string[] GetReaders(out IntPtr readercount);

But after run I can got readercount but the app got below error:

Cannot marshal 'return value': Invalid managed/unmanaged type combination.

What is wrong?

I did it by java and work perfectly. But I have problem with .Net.

Marshalling is almost never trivial but marshalling strings is always guaranteed to be complicated. Is that a std::string array that you're returning from your method? How's that allocated? — Mike Dinescu
– Mike Dinescu, Commented Jan 13, 2015 at 21:13

David Heffernan · Accepted Answer · 2015-01-13 21:20:25Z

2

It's impossible to call that method with p/invoke. That's because you cannot marshal C++ classes using p/invoke. And string is, presumably, std::string.

You'll need to either use a C++/CLI wrapper, or re-design the C++ interface to be p/invoke friendly.

answered Jan 13, 2015 at 21:20

David Heffernan

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