Pass a string as argument from C# to callback function in C++

I am writing a C# dll wrapper to wrap a third party C# dll. I also need to expose this as Java methods for which I am using an intermediate C++ layer which wraps my C# dll and provides a JNI mechanism to expose the same using java.

However, I am having an issue in passing string as argument to the callback function when its invoked in C++. Here is the code.

#include "stdafx.h"
#include "JavaInclude.h"
#include <iostream>
#using "Class1.netmodule"
#using <mscorlib.dll>

using namespace std;
using namespace System;

int CSomeClass::MemberFunction(void* someParam)
    cout<<"Yaay! Callback"<<endl;
    return 0;

static int __clrcall SomeFunction(void* someObject, void* someParam, String^ strArg)
    CSomeClass* o = (CSomeClass*)someObject;
    return o->MemberFunction(someParam);

JNIEXPORT void JNICALL Java_de_tum_kinect_KinectSpeechInit_initConfig
    (JNIEnv *env, jobject obj)
    array<String^>^ strarray = gcnew array<String^>(5);
    for(int i=0; i<5; i++)
            strarray[i] = String::Concat("Number ",i.ToString());

    CSomeClass o;
    void* p = 0;
    CSharp::Function(System::IntPtr(SomeFunction), System::IntPtr(&o), System::IntPtr(p), strarray);

Here is my C# class

using System;
using System.Runtime.InteropServices;

public class CSharp
    delegate int CFuncDelegate(IntPtr Obj, IntPtr Arg, string strArg);

    public static void Function(IntPtr CFunc, IntPtr Obj, IntPtr Arg, String[] pUnmanagedStringArray)
        CFuncDelegate func = (CFuncDelegate)Marshal.GetDelegateForFunctionPointer(CFunc, typeof(CFuncDelegate));

        for (int i = 0; i < pUnmanagedStringArray.Length; i++)
        string strArg = "Test String";
        int rc = func(Obj, Arg, strArg);

When I did Console::WriteLine(strArg); in my C++ dll, it just prints a blank string! Would really appreciate if anyone can help me as I am pretty new to all this.

Thanks, Deepak


The most likely issue is that C++ expects ANSI strings where as C# creates Unicodes ones.

So if you replace with this

delegate int CFuncDelegate(IntPtr Obj, IntPtr Arg, [MarshalAs (UnmanagedType.LPSTR)] string strArg); 

You can check out more information here:

Need Your Help

org-babel new language

emacs org-mode org-babel

I'd like to run some code through a binary via stdin and paste the output. The language is foma, is there a fast way for that or do I have to write my own definition? I've tried

How to access the accelerometer of a Windows Mobile device?

c++ qt windows-mobile accelerometer

I've successfully ported my Qt-based C++ application to my girlfriend's Windows Mobile device. (A Samsung Omnia 2.)

About UNIX Resources Network

Original, collect and organize Developers related documents, information and materials, contains jQuery, Html, CSS, MySQL, .NET, ASP.NET, SQL, objective-c, iPhone, Ruby on Rails, C, SQL Server, Ruby, Arrays, Regex, ASP.NET MVC, WPF, XML, Ajax, DataBase, and so on.