Delete keyword and Destructor problem

**almawajdeh** · 12-25-2010

Hi..
I have misunderstanding with delete keyword, specially with data structures programming, in the following code, does i have to delete the dynamic prt, or it will destruct automatically,
Please explain what is happen??
and thank you in advance

Code:

#include "iostream"
using namespace std;
template <class T>
class A
{ 
private:int *ptr;
public:
	
	A(){
	int *ptr=new int(9);
	cout<<"\nAAA\n";
	}
	 ~A()
	{
		cout<<"D "<<" ";
		delete ptr;
	}
	
};
void main()
{	A<int> a11;	
}

"this code doesn't work properly"

**tabstop** · 12-25-2010

No such thing in C++ as void main, of course.

Anything you new you must delete. The fun part is that you probably think that this line:

Code:

int *ptr = new int(9);

has something to do with your private ptr variable. It doesn't.

**Salem** · 12-25-2010

The problem is, you redeclare your int *ptr inside your ctor.
This makes your class member variable invisible (and uninitialised).
So when you come to delete it, it's garbage.

Code:

$ g++ -Wall foo.cpp
foo.cpp: In constructor ‘A<T>::A() [with T = int]’:
foo.cpp:21:   instantiated from here
foo.cpp:10: warning: unused variable ‘ptr’

Just do

Code:

ptr=new int(9);

**kmdv** · 12-25-2010

I'm wondering why you templated this class. You might want to do:

Code:

template <class T>
class A
{ 
private:
    T *ptr;
public:
    A()
    {
        ptr=new T(9);
	cout<<"\nAAA\n";
    }
    ~A()
    {
        cout<<"D "<<" ";
	delete ptr;
    }	
};

**Elysia** · 12-30-2010

Code:

#include <memory>

template <typename T>
class A
{ 
private:
    std::shared_ptr<T> m_ptr;
public:
    A()
    {
        m_ptr = std::make_shared<T>(9);
	std::cout << "\nAAA\n";
    }
    ~A()
    {
        std::cout << "D " << " ";
    }	
};

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