passing string type to C++

How do you pass on a simple string or byte array ....type to C# and get it back from C# in C++ ?

I have managed to do it with integer but with ANSI strings does not seem so simple.

from C# to c++

http://bytes.com/forum/thread250052.html

'Get' : cannot convert parameter 1 from 'char *' to 'struct tagSAFEARRAY *'

Code:

---

#include "stdafx.h"
#include "tchar.h"
#include <comutil.h>

#include <string>
// Import the type library.

//#import "..\ManagedDLL\bin\Debug\ManagedDLL.tlb" raw_interfaces_only
#import "C:\Mydot-net-projects\sManagedDLL\sManagedDLL\bin\Debug\sManagedDLL.tlb"
using namespace sManagedDLL;
int _tmain(int argc, _TCHAR* argv[])
{
    // Initialize COM.
    HRESULT hr = CoInitialize(NULL);

    // Create the interface pointer.
    ICalculatorPtr pICalc(__uuidof(ManagedClass));

    long lResult = 0;
        std::string str;

    // Call the Add method.
//    pICalc->Add(5, 10, &lResult);
    wprintf(L"The result1 is [%d]\n", pICalc->Add(5, 10));
        char p[10];


        char *szTemp = new char [1000];
        strcpy(szTemp,"Test");
    wprintf(L"The result2 is p=[%s]\n",pICalc->Get(szTemp) );


    // Uninitialize COM.
    CoUninitialize();
    return 0;
}

---

and in C#

Code:

---

using System;
using System.Collections.Generic;
using System.Text;

namespace sManagedDLL
{

    // Interface declaration.
    public interface ICalculator
    {
        int Add(int Number1, int Number2);
        string Get(char [] s);
    };
    // Interface implementation.
    public class ManagedClass : ICalculator
    {
        public int Add(int Number1, int Number2)
        {
            return Number1 + Number2+3;
        }
        public string Get(char[] s)
        {
            StringBuilder sBuffer = new StringBuilder(100);
            return sBuffer.ToString();
         
        }
    }
}

---

You pass strings in and out in C++ by using BSTRs - these are the COM standard strings.

See AllocSysString and FreeSysString in the C++ Win32 API.

Or _bstr_t (ATL) or CComBSTR (MFC) which are wrapper classes for BSTRs.

On the C# side of things you should do :

Code:

---

public string Get(IntPtr s)
{
    return System.Runtime.InteropServices.Marshal.PtrToStringAnsi(s);
}

---

char[] will be translated to a safearray of chars by default.

The return type in C++ since you're using #import will be a _bstr_t so you can't just pipe it into a printf : you need to convert it to a char * first e.g.

Code:

---

wprintf(L"The result2 is p=[%s]\n",static_cast<wchar_t *>(pICalc->Get(szTemp)) );

---

Or you can try

Code:

---

using System.Runtime.InteropServices;

string Get([MarshalAs(UnmanagedType.LPStr)] string input)
{
  return input;
}

---

which should work for char * arrays being passed from C++ but I've not tried it.

You should also assign [Guid] attributes to both your interface and your class otherwise everytime you re-register them they'll get a different COM Guid and cause all sorts of problems.

They should both also have the [ComVisible(true)] attribute to make sure they're exportable to COM.

Darwen.

Darwen;

You are A++ genius mate .
Thanks :thumb: