How to make a C++ class whose objects can only be dynamically allocated?

2.7

The problem is to create a class such that the non-dynamic allocation of object causes compiler error. For example, create a class ‘Test’ with following rules.

    Test t1;  // Should generate compiler error
    Test *t3 = new Test; // Should work fine

The idea is to create a private destructor in the class. When we make a private destructor, the compiler would generate a compiler error for non-dynamically allocated objects because compiler need to remove them from stack segment once they are not in use.
Since compiler is not responsible for deallocation of dynamically allocated objects (programmer should explicitly deallocate them), compiler won’t have any problem with them. To avoid memory leak, we create a friend function destructTest() which can be called by users of class to destroy objects.

#include <iostream>
using namespace std;

// A class whose object can only be dynamically created
class Test
{
private:
    ~Test() { cout << "Destroying Object\n"; }
public:
     Test() { cout << "Object Created\n"; }
friend void destructTest(Test* );
};

// Only this function can destruct objects of Test
void destructTest(Test* ptr)
{
    delete ptr;
    cout << "Object Destroyed\n";
}

int main()
{
    /* Uncommenting following following line would cause compiler error */
    // Test t1;

    // create an object
    Test *ptr = new Test;

    // destruct the object to avoid memory leak
    destructTest(ptr);

    return 0;
}

Output:

Object Created
Destroying Object
Object Destroyed

If we don’t want to create a friend function, we can also overload delete and delete[] operators in Test, this way we don’t have to call a specific function to delete dynamically allocated objects.

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