On Aug 27, 2012, at 4:05 PM, Gabriel Dos Reis wrote: > On Mon, Aug 27, 2012 at 1:48 PM, <paul_kon...@dell.com> wrote: >> I'm doing some checking of data structure layouts in different releases of >> our code -- which were produced by different releases of GCC (3.3.3 vs. >> 4.5.4). >> >> One difference I'm seeing that is puzzling is in the handling of base >> classes. Specifically, the case where a base class has padding at the end >> to fill it out to a multiple of the alignment. >> >> In GCC 3.3.3, when such a class is used as a base class, that padding is >> omitted, and the first derived class data member starts right after the last >> base class real (not pad) data member. In GCC 4.5.4, the base class is used >> padding and all, the first derived class data member starts after the >> padding of the base class. >> >> Which is correct? Or are both correct? This sort of thing is a potential >> cause of trouble if such a class is used as a container for persistent data. >> >> paul >> > > Is this message > > http://gcc.gnu.org/ml/gcc/2002-08/msg00874.html > > relevant to your case? > > -- Gaby
Yes, that looks like the exact case. And the mail thread seems to say that the "3.3.3" behavior I'm seeing is what G++ was doing at that time, as was HP -- but not Intel. So now we have it done differently in later compilers. I know this is changing data structure layouts in our code; I don't know yet if that is a problem (i.e., if it applies to layouts used in persistent data or in protocol messages). I assume there isn't some compiler switch I can use to control this behavior? paul