TITLE: Size of zero element arrays


PROBLEM: viren@wipro.wipsys.soft.net (Virendra Kumar Mehta)

Just out of curiousity, what is the sizeof() a zero length array?

A couple quick test programs I wrote tells me that

     typedef struct {char i[0];} ZZZ;
     main() {printf("%d\n",sizeof(ZZZ));}

the above had a size of 1 if I compile with a .cc extention (c++);
but size of 0 if I compile with a .c extention (c).


RESPONSE: jimad@microsoft.com (Jim Adcock), Microsoft Corporation, 1 Mar 94

ARM says you cannot statically define arrays of #elements == 0, however
you are allowed to dynamically allocate arrays of #elements == 0, so 
the static constraint makes no sense, IMHO.  In any case, the sizeof
an array = #elements * sizeof(element) "by definition" since the
sizeof(anything) is "by definition" the number of bytes that thing
takes *as an element in an array*.

Thus the sizeof() a zero length array by definition must be zero.
This is not the same as saying the number of bytes taken by a zero
length dynamic allocation is zero.  On the contrary, it is very common
for such to take on the order of 10 bytes of storage space "wasted".