Trouble using .NET dll in Borland C++ Builder 4

[SteelNetNob]

I have created a COM callable DLL in C# .NET 2.0 and created a TLB
from the assembly using the .NET regasm tool.

In Borland C++ Builder 4.0 I go to Project->Import Type Library-> and
find my DLL's type library there and click "Ok" to import it.


BCB creates an HardwareCheck_TLB.cpp & HardwareCheck_TLB.h file.


In a cpp file of the project I want to use the DLL I put:
#include "HardwareCheck_TLB.h"
at the top.


Then in code if I try to declare an object of that type in code:
IHardwareCheck hc = new IHardwareCheck();


I get the following compiler error:
[C++ Error] Unit1.cpp(22): E2352 Cannot create instance of abstract
class 'IHardwareCheck'.
[C++ Error] Unit1.cpp(22): E2353 Class 'IHardwareCheck' is abstract
because of '__stdcall IHardwareCheck::IsExpress(wchar_t * *,TOLEBOOL
*) = 0'.


Anybody have any ideas how to get rid of this error?


Thanks!

[weaknessforcats]

You cannot create objects of classes that have pure virtual functions.

You are supposed to create a derived object (which has no pure vrtual functions) and assign the address of that object to a base class pointer (like I HardwareCheck). Then you use IHardwareCheck->etc... to call member functions on that derived object.

[SteelNetNob]

Can you please provide an example of the syntax of creating such a derived class or at least a link which illustrates this?

Thanks!

[weaknessforcats]

Here you go:

class Shape
{
    public:
       virtual void draw() = 0;
};
class Circle : public Shape
{
     public:
        virtual void draw();
};
void Circle::draw()
{
    cout << I am a Circle" << endl;
}
 
int main()
{
    //Shape* s = new Shape;  //ERROR. Cannot create Shape objects
    Shape* s = new Circle;
    s->draw();   //calls Circle::draw()
}

This is fundamental C++ polymorphism. Any C++ textbook will discuss this.

[SteelNetNob]

thank you I understand from back in college...

what I don't understand is which side do I do this on? Do I do it on the C# .NET side where my dll is written, or do I do it on the Borland C++ Builder side where I actually will be using the dll.

Have you ever actually done this before (i.e. used a C# dll with Borland C++ Builder)??

Thanks for all inputs so far.

[weaknessforcats]

It looks like IHardwareCheck is an interface of a C++ COM class.

I assume you know how to use COM. If not, you have a big learning curve here. Especially since this uses non-virtual multiple inheritance

You create your COM object by calling CoCreateInstance with the GUID for your COM class and then use a call to QueryInterface using the GUID for IHardwareCheck. That should return a pointer to the IHardwareCheck interface. Now you can use IHardwareCheck methods.

This is all done on the C++ side.

[nirdesh]

The problem is in using the tlb created. Try using . It works with me.

//------------------Implementation Method1----------------------------

IHardwareCheckPtr pIDotnetObj;
pIDotnetObj = CreateComObject(CLSID_HardwareCheck);
pIDotnetObj->ShowDialog();

//--------------------Implementation Method2---------------------------


CoInitialize(NULL);

IHardwareCheckPtr pDotNetCOMPtr;
HRESULT hRes = pDotNetCOMPtr.CreateInstance(CLSID_HardwareCheck );
if (hRes == S_OK)
{
pDotNetCOMPtr->ShowDialog2();
}

CoUninitialize ();

[SteelNetNob]

Great thanks a ton for all the help given here.

I really appreciate it.

I was told before that you couldn't use a .NET DLL in Borland C++ Builder 4, but now this proves that person was wrong.

I bet the same could be done in Delphi 3 using the same .NET dll.