Re: Size and pack

[byhoe@greenlime.com (Adrian Hoe)]

"Jeff Creem" <jeff@thecreems.com> wrote in message news:<nHRD7.162473$vq.40258001@typhoon.ne.mediaone.net>...
> OK.. I know I am going to regret this since whenever I question Robert I
> usually am wrong however
> without using the complete context of this thread, I believe Roberts
> statement is actually
> 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;
> 
> 
> The pragma pack is needed I believe because the rep spec on My_Array can
> be rejected without it (At least it has been rejected by some compilers and
> I forget
> the exact rule but it had something to do with the final rep spec not being
> allowed to
> change the layout of the items within the array).
> 
> Having said that VADS used to compile this without the pragma pack. Green
> Hills did not.
> I *THINK* GNAT does allow it to go through without the rep spec for several
> versions now.


But, why the differenct implementation by these compilers' vendors? I
thought Ada is a standardized language regardless of platforms. Of
course, a problem like whether to use "pragma pack" or not in the
above Jeff's example "supposed" not to arise if Ada is standardized.

Oh... I am getting quite confusing now, and not to mention Ada
newbies!



> 
> "Robert Dewar" <dewar@gnat.com> wrote in message
> news:5ee5b646.0110301750.38ba5bfd@posting.google.com...
> > john.mccabe@emrad.com.nospam (John McCabe) wrote in message
>  news:<3bc41989.4285341@news.demon.co.uk>...
> > > Your best bet would be to use as many representation attributes as are
> > > necessary. In general I would use both a representation clause and
> > > pragma pack
> >
> > No, that's pointless, if you use a complete rep clause, then it is
> > redundant to use pragma Pack since it won't have
> > any effect.