Allocating memory. constructor being called

Hello,

I am trying to gain access to a int that I have created with new from the constructor of the base class.
I would like to access this from my derived class. However, when the constructor of the derived class gets
called it will call the base class constructor a second time and allocate another memory location.

When I try and get the pointer to the int I get a different value to the one that is assigned.

Any thing I am doing wrong?

Many thanks,

Code:

---

#ifndef TBBoardService_INCLUDED
#define TBBoardService_INCLUDED

class TBBoardService
{
public:
        TBBoardService();
        ~TBBoardService();
       
        void handle(int *handle);
        void open_library();
        int* hLibrary(){ return _lib_handle;}

private:
        int *_lib_handle;
};
#endif // TBBoardService_INCLUDED

---

Code:

---

#include "TBBoardService.hpp"

void TBBoardService::handle(int *handle)
{
        *handle = 123456;
}

void TBBoardService::open_library()
{
        handle(_lib_handle);               
}

TBBoardService::TBBoardService() : _lib_handle(0)
{
        _lib_handle = new int;

}

TBBoardService::~TBBoardService()
{
        delete _lib_handle;
}

---

Code:

---

#include <iostream>
#include "TBIsdnBoardService.hpp"

void TBIsdnBoardService::svc()
{
        std::cout << "Start SVC" << std::endl;

        int hLib = *(hLibrary()); // cannot get the correct value here

        std::cout << "hLib: " << hLib << std::endl;
}

---

Code:

---

#include <iostream>
#include "TBBoardService.hpp"
#include "TBIsdnBoardService.hpp"

int main(int argc, char** argv)
{
        TBBoardService *boardservice = new TBBoardService();
        boardservice->open_library();
        std::cout << "_lib_handle: " << *(boardservice->hLibrary()) << std::endl;

        TBIsdnBoardService *isdn = new TBIsdnBoardService();
        isdn->svc();

        getchar();

        return 0;
}

---

What do you expect to get, and what do you get? You've got an int *. New does value initialization, doesn't it? Shouldn't you get 0? (And if it's not value initialized, who knows what you're going to get.)

I'm not sure I understand the problem.

Your base class default constructor (the one with no arguments) allocates a new int.

The derived class constructor is required to invoke a destructor of the base class (as the base class "part" of an object has to be constructed in order for the derived class to work). If the derived class constructor invokes the default constructor, a new int will be allocated every time a derived class object is instantiated - each distinct instance of the derived class includes data of a distinct instance of the base class.

Which would suggest you're seeing what you should.

If you're not seeing what you expect, your expectations are wrong.

In particular, in your main() function, the object named isdn will not magically access the _lib_handle member in the object named boardservice. The instance of TBBoardService named boardservice is a distinct object from the TBBoardService within isdn.