Simple resizable array
I see a couple of problems:


If you ever shrink the array, the loop for copying the elements will overrun the bounds of newdata because the index runs from 0 to mSizeOld.
You don't store the size of the array in the class, so code like this will lose data:

ResizeableArray&lt;Thing&gt; a;
a.resize(0, 10);
// Populate the array
a.resize(0, 11);
// Now a is empty again because resize() uses the first argument.


This might be intentional &mdash; to allow you to start over with a fresh set of data &amp;mdash but if so, resize() should be commented to say that.