将本机指针函数传递给C＃方法

Question

I have a C++ project containing a nonmanaged class method used to display string in a user interface :

void MyProject::displayIHM(std::string mystring);

This project is compiled with /clr because it calls another one made with C#/.NET 4.0. The goal of the .NET project is to make heavy computation tasks. During computation, we want to get back from it some information to the user interface.

My idea was to create two new methods in the C++-cli project :

void MyProject::displayFromDotNet(String^ mystring)
{
      displayIHM(ToStdString(mystring));
}

string ToStdString ( String ^ s)
{
   const char* chars = (const char*)(Marshal::StringToHGlobalAnsi(s)).ToPointer();
   string os = chars;
   Marshal::FreeHGlobal(IntPtr((void*)chars));
   return os;
}

Until now, everything is ok but now the difficult part : how to provide displayFromDotNet to the .NET project. My idea was to provide a function pointer in the constructor of the .NET class and then to launch the process :

void (MyProject::*pointeurFunc)(String^) = &MyProject::displayFromDotNet;
ComputationProject^ kernel = gcnew ComputationProject((this->*pointeurFunc)); 
kernel->Compute();

The second line does not work. The constructor of ComputationProject has a IntPtr parameter but I do not know if I can convert a function pointer to an IntPtr^ in C++. I also made some attempts using Marshal::GetDelegateForFunctionPointer but it could not compile.

I do not know what to do, any help would be appreciated!

EDIT : yes ComputationProject is my C#/.NET project. The error with line 2 is "cannot convert parameter 1 from 'overloaded function type' to 'System::IntPtr'".

Answer 1

I finally find a (ugly) way.

My main problem was I could not pass a method pointer to C# because it is not a real function pointer (so I cannot cast it to IntPtr). I decided to create a second class containing a static MyProject object and a static method calling displayIHM on the static object :

class StaticMyProject
{
public :
    static MyProject staticObject;
    static void DisplayInIHM(char *);
}; 

In cpp :

MyProject StaticMyProject::objetStatique;

void StaticMyProject::DisplayInIHM(char *message)
{
    std::string message2(message);
    staticObject.displayIHM(message2);
}

Now for calling Compute method of ComputationProject, I modified the code like this :

StaticMyProject::objetStatique = *this;
void (*funcPointer)(char*) = StaticMyProject::DisplayInIHM;
ComputationProject^ kernel = gcnew ComputationProject((IntPtr)funcPointer);
kernel->Compute();

And in my ComputationProject.cs :

public class ComputationProject
    {
        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        public delegate void FunctionPointer([MarshalAs(UnmanagedType.LPStr)]string message);

        public readonly FunctionPointer DisplayMethod;

        public ComputationProject(IntPtr ptr)
        {
            this.DisplayMethod = (FunctionPointer)Marshal.GetDelegateForFunctionPointer(ptr, typeof(FunctionPointer));                       
        }

        public int Compute()
        {            
            this.DisplayMethod("Beginning computation...");
            ...
        }
    }