🚀 go-pugleaf

In article 96Feb27175316@kronecker.mitre.org, mgb@kronecker.mitre.org (G. Mike Butler D054) writes:
>According to the ARM section 5.3.3:
>     "operator new() can be called with the argument
>      zero.  Repeated such calls return pointers to
>      distinct objects."  
     
>But when I execute the following:
>    #include <isotream.h>
>    main()
>    {
>      struct foo { char a[1024]; };
>      foo *p = new foo[0];
>      foo *q = new foo[0];
>
>      cout << (void *)p << " " << (void *)q << endl;
>    }

>I get
>    0x338d8 0x338e8

>While these are distinct pointers, the pointers refer to overlapping
>objects.

No, they don't. You asked for an array of zero elements. For an array A
of n elements, you may access any elements from A[0] through A[n-1].
In addition, the address of A[n] is a valid address for comparisons,
but you may not access any object at that address, because there isn't
one at that address. Substitute 0 for n, and you find that the
expression A[i] is invalid for all values of 'i', but &A[0] is a valid
address expression, as long as you don't try to access the (non-existant)
object at that address.

Therefore, as long as the values of p and q are different, all
requirements have been satisfied. You can't usefully describe them as
pointing to "overlapping objects". There are no objects at all, and
you can't dereference the pointers.

---
Steve Clamage, stephen.clamage@eng.sun.com




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