Delete keyword and Destructor problem

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;       
}

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"this code doesn't work properly"

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.

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);

---

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;
    }       
};

---

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 " << " ";
    }       
};

---