Question

So in C++ if I create an object useing new I should always deallocate it using delete
For example

Segment::Segment(float length)
{
    segmentLength = length;

    angle = 0.0f;
    x = Rand::randFloat(1.0f, 1.5f);
    y = Rand::randFloat(1.0f, 1.5f);

    vx = Rand::randFloat(0.0f, 1.0f); 
    vy = Rand::randFloat(0.0f, 1.0f);
    prevX = Rand::randFloat(0.0f, 1.0f);
    prevX = Rand::randFloat(0.0f, 1.0f);
};

And lets say I use it like this in another class such as,

this._segmentObject = Segment(2.0f);
this._segmentPointer = new Segment(2.0f);

In the destructor of that class, I know I should call delete on the this._segmentPointer, however how do I make sure memory is deallocated for the other one?

Answer 1

Things not allocated with new, new[] or the malloc family should be destructed and “freed” when the object goes out of scope.

Often this simply means that that the code has reached the end of the block it was declared it or that the object that it was in was destructed (one way or another).

To see this in action, you can do something like this:

struct C {
    C()  { std::cout << "C()" << std::endl; }
    ~C() { std::cout << "~C()" << std::endl; }
};

struct B {
    B()  { std::cout << "B()" << std::endl; }
    ~B() { std::cout << "~B()" << std::endl; }
private:
    C c_;
};

struct A {
    A()  { std::cout << "A()" << std::endl; }
    ~A() { std::cout << "~A()" << std::endl; }
};

int main() {
    B *b = new B; // prints "B()", also constructs the member c_ printing "C()"
    { // starts a new block
        A a; // prints "A()";
    } // end of block and a's scope, prints "~A()"

    delete b; // prints "~B()", also destructs member c_, printing "~C()"
}

Note: that if we did not do delete b, the “~B()” and “~C()” would never print. Likewise, if c_ were a pointer allocated with new, it would need to be delete‘d in order to print “~C()”