Re: Dynamic memory management, straightening my understanding of its details

Hi there,
I'm trying to understand the details of the dynamic memory management.

These are the various sections I've read these days:

1.7 [intro.memory]
3.7.3 [basic.stc.dynamic]
5.3.4 [expr.new]
5.3.5 [expr.delete]
12.5 [class.free]
18.4.1 [lib.new.delete]
20.4 [lib.memory]

The last sections above are quite technical and wide, I'm still far from
having any decent grasp on them.

Before going on I need to clear out if what I understood so far is correc=

I wrote the following at the best of my comprehension and, as far as I
can tell, it should be a well-defined C++ program, please tell me if and
where I've gone off the track:

//-------

#include <iostream>
#include <new>

using namespace std;

const int n = 2;

void int_test() {

     cout << " # int_test()" << endl;

     // allocate
     int* ptr = static_cast<int*>(
                    operator new(sizeof(int))
                );

     // non-initialized creation
     new(ptr) int;

     // prints garbage
     cout << *ptr << endl;

     // zero-initialized creation
     new(ptr) int();

     // prints zero
     cout << *ptr << endl;

     // deallocate
     operator delete(ptr);

     cout << endl << " # int_test(), array version" << endl;

     // allocate
     int* arr_ptr = static_cast<int*>(
                        operator new[](n * sizeof=

                    );

     // non-initialized creation
     new(arr_ptr) int[n];

     // prints garbage values
     for (int i = 0; i < n; ++i) {
         cout << arr_ptr[i] << endl;
     }

     // zero-initialized creation
     new(arr_ptr) int[n]();

     // prints zeros
     for (int i = 0; i < n; ++i) {
         cout << arr_ptr[i] << endl;
     }

     // deallocate
     operator delete[](arr_ptr);

}

struct POD {
     int data;

};

void POD_test() {

     cout << " # POD_test()" << endl;

     // allocate
     POD* ptr = static_cast<POD*>(
                    operator new(sizeof(POD))
                );

     // non-initialized creation
     new(ptr) POD;
     // prints garbage
     cout << ptr->data << endl;

     // zero-initialized creation
     new(ptr) POD();
     // prints zero
     cout << ptr->data << endl;

     // deallocate
     operator delete(ptr);

     cout << endl << " # POD_test(), array version" << endl;

     // allocate
     POD* arr_ptr = static_cast<POD*>(
                        operator new[](n * sizeof=

                    );

     // non-initialized creation
     new(arr_ptr) POD[n];

     // prints garbage values
     for (int i = 0; i < n; ++i) {
         cout << arr_ptr[i].data << endl;
     }

     // zero-initialized creation
     new(arr_ptr) POD[n]();

     // prints zeros
     for (int i = 0; i < n; ++i) {
         cout << arr_ptr[i].data << endl;
     }

     // deallocate
     operator delete[](arr_ptr);

}

struct Base {
     virtual int data() const = 0;
     virtual ~Base() {}

};

class Derived : public Base {
public:
     Derived(int i = 123) : ptr(new int(i)) {
         cout << "Derived::Derived(int)" << endl;
     }
     Derived(const Derived& d) : ptr(new int(*d.ptr)) {
         cout << "Derived::Derived(const Derived&)" << endl;
     }
     Derived& operator=(const Derived& d) {
         cout << "Derived::operator=(const Derived&)" << endl=

         *ptr = *d.ptr;
         return *this;
     }
     ~Derived() {
         cout << "Derived::~Derived()" << endl;
         delete ptr;
     }
     int data() const {
         return *ptr;
     }
private:
     int* ptr;

};

void Derived_test() {

     cout << " # Derived_test()" << endl;

     // allocate
     Derived* ptr = static_cast<Derived*>(
                        operator new(sizeof(Deriv=

                    );

     // according to 12.1p8 [class.ctor]
     // this calls Derived::Derived(123)
     new(ptr) Derived;

     // prints 123
     cout << ptr->data() << endl;

     // call destructor
     ptr->~Derived();

     // calls Derived::Derived(321)
     new(ptr) Derived(321);

     // prints 321
     cout << ptr->data() << endl;

     // call destructor
     ptr->~Derived();

     // deallocate
     operator delete(ptr);

     cout << endl << " # Derived_test(), array version" << endl;

     // allocate
    Derived* arr_ptr = static_cast<Derived*>(
                            operator new[](n =

                        );

     // calls Derived::Derived(123) n-times
     new(arr_ptr) Derived[n];

     // prints 123 n-times
     for (int i = 0; i < n; ++i) {
         cout << arr_ptr[i].data() << endl;
     }

     // call destructors
     for (int i = n; i > 0; --i) {
         arr_ptr[i-1].~Derived();
     }

     // calls Derived::Derived(123) n-times
     new(arr_ptr) Derived[n]();

     // prints 123 n-times
     for (int i = 0; i < n; ++i) {
         cout << arr_ptr[i].data() << endl;
     }

     // call destructors
     for (int i = n; i > 0; --i) {
         arr_ptr[i-1].~Derived();
     }

     // deallocate
     operator delete[](arr_ptr);

}

int main() {

     int_test();

     cout << "===========" << endl;

     POD_test();

     cout << "===========" << endl;

     Derived_test();

     return 0;

}

//-------

Thank you for your attention.

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