Originally posted by the one I mean, I do de-reference 'a pointer to array' to 'an array'; and the size of array is very large( e.g. 100.000 );
Not quite. T* as a type is just a pointer to T, it's not an array of T. So you have a T**, which is a pointer to a pointer of T, you dereference it and this will become only a pointer to T.

So the dereference operation only works on the pointer and hence it is quite fast.