Delete array pointer c++ when increase pointer?

Question

I have:

int *ptr = new int[8];
delete[] ptr;  //  it ok, all ptr is delete;

but if I have:

int *ptr = new int[8];
ptr++; 
delete[] ptr;

My question:

Does delete[] delete all ptr from ptr[0] to ptr[7] or just from ptr[1] to ptr[7] ? And, if it deletes from ptr[1] to ptr[7] , how does delete[] know the real size to delete this time?

Answer 1

Neither; it's undefined behaviour, which usually means it'll crash the program.

The pointer you pass to delete[] must be one that was previously returned from new[] . No exceptions*. new[] returned a pointer to the first element of the array, so you must pass a pointer to the first element of the array to delete[] .

* the only exception is that you can pass a NULL pointer, in which case it will do nothing.