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?

You can't release just a part of an allocation - all or nothing are your only options. — molbdnilo
– molbdnilo, Commented Nov 20, 2015 at 12:13

Stack Exchange Broke The Law · Accepted Answer · 2015-11-20 12:10:31Z

18

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.

answered Nov 20, 2015 at 12:10

Stack Exchange Broke The Law

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