Size of array (new[])

Question

In debug heap I can get size of array, which was created by new[]:

int size = *((int *)((char *)ptr - 16));

It is working correctly if the size of the array is less than 28 (but I don't know why? 0_0).

Does this trick working in release mode (not using debug heap)?

How I can get size of the array (100% working and stable)?

Answer 1

You are relying on an implementation detail. That's how your particular implementation stores the size of the memory region where the array is placed. As you already see, the size of the memory region may be bigger than the size of the allocated array.

If you need to know the size of an array allocated with new[], you'll have to keep that value around.