Hello Ze'ev,
unless the structure is defined with the nonstandard extension Packed
(or _Packed, I don't recall it exactly), all ints or longs will be
aligned on
a 4 byte boundary, that is, in a sequence of int, short, int, short, you
will
get two padding bytes after every short field (which is in fact 2 bytes
long).
Same goes for PL/1 with a sequence of BIN FIXED(31) and BIN FIXED(15)
fields. The rules for alignment with PL/1 are more complicated than with C.
Structures in C always start with the highest needed alignment required
inside
the structure, while in PL/1 there is some work done to start the
structure at
an offset which minimizes the padding bytes in the middle of the structure
(short story, the long explanation in the PL/1 books needs many pages).
You can synchronize alignment between PL/1 and C, if you put a dummy
double precision field (which has alignment requirement of 8) in front
of the structure.
The the two languages do the same. A similar technique should work for
COBOL, too.
Kind regards
Bernd
Am 23.02.2015 um 03:44 schrieb Ze'ev Atlas:
__off_t is clearly defined earlier as a 32 bit entity but mbstate_t is defined
as short which I assumed is a 16 bit entity. Either short is NOT 16 bits but
32 bit entity as well, or the C compiler leaves 2 bytes of zeroes in order to
keep the correct integral boundary. However, in REAL LIFE there are 32 bits
between rm_so and rm_eo. I did not bother to investigate too much ...
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