Re: Size and pack

[Jeffrey Carter <jrcarter@acm.org>]

Jeff Creem wrote:
> 
> a little too broad. There ARE indeed times when you want a pragma pack and a
> rep spec. Not for the record case but for arrays of items that have been rep
> spec'ed.
> 
> for example, the code fragment
> 
> type My_Type is range 0 .. 3;
> for My_Type'size use 2;
> 
> type My_Array is array (1 .. 4) of My_Type;
> pragma Pack (My_Array); -- Without this the following could fail
> for My_Array'size use 8;

Generally a compiler would use 4 bytes (or storage units) for My_Array,
and without something to tell the compiler to use less storage for each
component the size clause should be rejected. However, one can replace
the pragma Pack with

for My_Array'Component_Size use My_Type'Size;
for My_Array'Size use My_Array'Length * My_Type'Size;

to obtain the same effect without relying on Pack, which is allowed to
be ignored.

-- 
Jeff Carter
"We call your door-opening request a silly thing."
Monty Python & the Holy Grail