int always 32 bits on all platforms?

[BCS]

Hello aJ,

>> In D, both type size and alignment have the same defaults on all
>> platforms.
>> 
> That must be some kind of magic considering that only some platforms
> require alignment on certain (word, dword, etc.) boundaries.

OK scratch alignment, I don't know what I was thinking there. 

> 
>> If desired, alignment can be explicitly controlled with the align
>> attribute. Similarly, use of specific types control sizes.
>> 
> Tell me, in D, can I have all the members of the following struct be
> byte-aligned and still access and use the members directly on all
> platforms without some kind of  "seqfault"(?):

Clearly if your CPU doesn't like to unaligned reads you are going to have 
problems with unaligned data members. In that cases you have several options:

1) if you don't really care much about the offsets, let DMD do it's thing
2) if you must have some given offsets, force it with align and live with 
the results because you're sunk
3) if you just need the same offset on a set of know systems, manually find 
something that works and force that with align (no compiler could help you 
here unless it know about all the system you care about)
4) if you just need the same offset on all system and you don't know what 
system will be used, see 2 because you're sunk.

> So did I just "summarize" the extent to which guaranteed basic type
> widths can be exploited, in that the design of ABC is always a "no no"
> and the design of CDE is very likely to work reliably across a wide
> range of designated platforms?
> 

I'm not very up on these issues but in short, you can let DMD do it's thing 
and get good result on any given system or you can force some alignment and 
get binary compatibility across systems. This is the same as in C. What D 
gives you (or takes away) is issues about int being one size on one system 
and another size of a different system.