c++ - Does this type of memory get allocated on the heap or the stack?

Question

In the context of C++ (not that it matters):

class Foo{
    private:
        int x[100];
    public:
        Foo();
}

What I've learnt tells me that if you create an instance of Foo like so:

Foo bar = new Foo();

Then the array x is allocated on the heap, but if you created an instance of Foo like so:

Foo bar;

Then it's created on the stack.

I can't find resources online to confirm this.

Answer 1

Given a slight modification of your example:

class Foo{
    private:
        int x[100];
        int *y;
    public:
        Foo()
        {
           y = new int[100];
        }
        ~Foo()
        { 
           delete[] y; 
        }

}

Example 1:

Foo *bar = new Foo();

• x and y are on the heap:
• sizeof(Foo*) is created on the stack.
• sizeof(int) * 100 * 2 + sizeof(int *) is on the heap

---

Example 2:

Foo bar;

• x is on the stack, and y is on the heap
• sizeof(int) * 100 is on the stack (x) + sizeof(int*)
• sizeof(int) * 100 is on the heap (y)

Actual sizes may differ slightly due to class/struct alignment depending on your compiler and platform.