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copied!<ol> <li>Do not make assumptions about the size of data-types, they are implementation dependent.</li> <li><code>MyClass *t1</code> defines an uninitialized pointer. Dereferencing it invokes <a href="http://en.wikipedia.org/wiki/Undefined_behavior" rel="noreferrer">undefined behavior</a>.</li> <li><code>t1 = (MyClass *)new MyClass;</code> allocates memory on the heap and creates a new object. If this memory does not get deallocated using <code>delete</code>, there will be a memory leak. Also, you do not need the cast there, <code>t1 = new MyClass();</code> suffices.</li> </ol> <p><strong>Edit:</strong> About allocation. </p> <pre><code>MyClass *t1 = NULL; </code></pre> <p>declares a pointer to a <code>MyClass</code>-object, but it does not create the object. This pointer is initialized to point to <code>0</code>. Now when you do</p> <pre><code>t1 = new MyClass(); </code></pre> <p>the operator <code>new</code> creates a new instance of <code>MyClass</code> and assigns the address of that object to <code>t1</code>. You can now work with that object through <code>t1</code>:</p> <pre><code>t1->doStuff(); </code></pre> <p>You can even create more pointers that point to the same object:</p> <pre><code>MyClass *t2 = t1; </code></pre> <p>Now <code>t2</code> and <code>t1</code> point to the same object. When you are done with the object, just do:</p> <pre><code>delete t1; </code></pre> <p>(<code>delete t2</code> would have the same effect). Now the object is destroyed, but the pointers still point to the same address (which is not safe anymore). Doing</p> <pre><code>t2->doStuff(); </code></pre> <p>after the <code>delete</code> invokes undefined behavior. If we go back to before the delete, consider this:</p> <pre><code>t1 = NULL; t2 = NULL; </code></pre> <p>Now we do not have the address of the object we created anymore, so we cannot call <code>delete</code> on it. This creates a memory leak. This hopefully gives you some understanding of what is going on. Now forget all this and read about <a href="http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization" rel="noreferrer">RAII</a>.</p>

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