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copied!<pre><code>A a = *(A *)new B(); a.func(); </code></pre> <p>Here's what happens in this code, step by step:</p> <ul> <li><code>new B()</code>: a new object of type B is allocated on the free store, resulting in its address</li> <li><code>(A*)</code>: the address of the object is cast to <code>A*</code>, so we have a pointer of type <code>A*</code> actually pointing to an object of type B, which is valid. All OK.</li> <li><code>A a</code>: here the problems start. A new <strong>local object</strong> of type A is created on the stack and constructed using the copy constructor <code>A::A(const A&)</code>, with the first paremeter being the object created before.</li> <li>The pointer to the original object of type B is lost after this statement, resulting in a memory leak, since it was allocated on the free store with <code>new</code>.</li> <li><code>a.func()</code> - the method is called on the (local) object of class A.</li> </ul> <p>If you change the code to:</p> <pre><code>A& a = *( A*) new B(); a.func(); </code></pre> <p>then only one object will be constructed, its pointer will be converted to pointer of type <code>A*</code>, then dereferenced and a new <strong>reference will be initialized with this address</strong>. The call of the virtual function will then be dynamically resolved to <code>B::func()</code>.</p> <hr> <p>But remember, that you'd still need to free the object since it was allocated with <code>new</code>:</p> <pre><code>delete &a; </code></pre> <p>Which, by the way, will only be correct if A has a virtual destructor, which is required that B::~B() (which luckily is empty here, but it doesn't need to in the general case) will also be called. If A doesn't have a virtual destructor, then you'd need to free it by:</p> <pre><code>delete (B*)&a; </code></pre> <hr> <p>If you would want to use a pointer, then that's the same as with the reference. Code:</p> <pre><code>A* a = new B(); // actually you don't need an explicit cast here. a->func(); delete (B*)a; // or just delete a; if A has a virtual destructor. </code></pre>

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