How can I boost::bind to a member of a managed class which passes and returns a std::string?

Question

I\'m trying to do something very similar to this but I\'m struggling to pass the string to/from the callback.

This is a pared down version of the code I\'m trying to run

Answer 1

Solved it with a bit of experimentation and some more detailed examination of the docs on different forms of bind.

This is the resulting code which works as expected:

using namespace System;
using namespace System::Runtime::InteropServices;

#pragma unmanaged

// The unmanaged boost function prototype the native library wants to bind to
typedef boost::function<std::string(const std::string&)> MyNativeCallback;

// The unmanaged library I'm trying to wrap
class MyUnmanagedClass
{
    public:
        MyUnmanagedClass() {}

        void RegisterCallback(MyNativeCallback callback);
};

typedef std::string(__stdcall *ChangeCallback)(std::string);
public delegate std::string ChangeHandler(std::string);

#pragma managed

// The managed callback we'll eventually trigger if all this works.
public delegate std::string ManagedHandler(const std::string&);

// A managed wrapper to bridge the gap and provide a managed call in response to the unmanaged callback
public ref class MyManagedClass
{
protected:

    MyUnmanagedClass* m_responder;

public:
    event ManagedHandler^ OnChange;

public:
    MyManagedClass():
        m_responder(new MyUnmanagedClass())
    {
        // Example code I'm trying to adapt from here: http://stackoverflow.com/questions/163757/how-to-use-boostbind-in-c-cli-to-bind-a-member-of-a-managed-class
        ChangeHandler^ handler = gcnew ChangeHandler(this, &MyManagedClass::HandleRequest);
        GCHandle gch = GCHandle::Alloc(handler);
        System::IntPtr ip = Marshal::GetFunctionPointerForDelegate(handler);
        ChangeCallback cbFunc = static_cast<ChangeCallback>(ip.ToPointer());

        MyNativeCallback handlerToBind = boost::bind<std::string>(cbFunc, _1);
        m_responder->RegisterCallback(handlerToBind);
    }

    std::string HandleRequest(const std::string& s)
    {
        return OnChange(s);
    }
};