Question about array new placement in C++

Question

I have question about new placement of array in c++. below code is a sample code that i made.

#include <vector>
#include <iostream>
class Point
{
    int x,y;
    public:
        Point():x(0), y(0){std::cout<<"Point() : "<<this<<std::endl;}
        void print(){std::cout<<x<<":"<<y<<std::endl;}
        Point(int a, int b) :x(a), y(b){std::cout<<"Point(int,int) : value & addr "<<a<<":"<<b<<" ~ "<<this<<std::endl;}
        ~Point(){std::cout<<"~Point() : "<<this<<" "<<x<<":"<<y<<std::endl;}
};

int main()
{
    // multiple allocation
    void* mem_ptr_arr = operator new(sizeof(Point)*3);
    for(int i=0; i<3; i++)
        new( mem_ptr_arr+sizeof(Point)*i ) Point(i,i);

    Point* ref_ptr_arr = static_cast<Point*>(mem_ptr_arr);
    // delete process
    for(int i=0; i<3; i++)
        (ref_ptr_arr+i)->~Point();
    operator delete(ref_ptr_arr);
    
    Point* new_ptr = new Point[3]{};
    delete[] new_ptr;

    return 0;
}

I want to duplicate functionality of new and delete operation. So break down each operation like below

1. new -> operator new + new(some_ptr) Constructor
2. delete -> Obj.~Destructor + delete(some_ptr) My question is, Is it correct usage of new placement of array(ref_ptr_arr)? When i debug some memory, they do not use same heap address after delete previous pointer.

Answer 1

I would simplify this way: First, just allocate the array with a low level function like malloc() or mmap(), brk() and dispose of it accordingly. It helps to keep the two worlds separated.

Second, when calling placement new you do not necessarily need to take that pointer if you already have it.

And last it looks like you are doing void pointer arithmetic and that was banned.

    // multiple allocation
    Point* points = (Point*)std::malloc(sizeof(Point)*3);
    for(int i=0; i<3; i++)
        new ( &points[i] ) Point(i,i);

    // delete process
    for(int i=0; i<3; i++)
        points[i].~Point();
    std::free( points );