🚀 go-pugleaf

In article <1992Nov6.171236.1394@rei.com>, fox@rei.com (Fuzzy Fox) writes:
|> >>>In your data declarations, if you do not specifically specify the
|> >>>keyword far, then the declaration is left in the default data
|> >>>segment, which can be a problem if you have more than 64k of global
|> >>>data.
|> 
|> This is true except in BC++ 3.1, where an option can be set which forces
|> all data declarations larger than a certain threshold to be
|> automatically moved into another segment.  The option is -Ff=nnnn, I
|> believe.  I use -Ff=1024 in all my programs.  In the IDE, this option is
|> set as the "Automatic Far Data" option and threshold.
|> 
|> >If you want to have arrays or structures that explicity
|> >store > 64k of data in one instance then you have to use the HUGE
|> >model,
|> 
|> You do not have to use huge model, you just need to use the 'huge'
|> keyword when declaring the data item.  In fact, a common misconception
|> is that the Huge model forces all pointers to be huge by default.  This
|> is not true.  Huge model is just like Large model, except that each
|> individual source file gets its own data segment automatically.  A
|> single source file program will compile exactly the same under Huge and
|> Large models.

I believe it is the case that virtual function table pointers are 4 bytes in the
huge model as opposed to 2 bytes in the large model. This is because in the huge
model they point to "any old" data segment whereas in the large model they point
to the "default" data segment, so the segment information is not required in the
latter case. Hence the compilation of a huge model program can be different and
in particular you will probably get linkage problems if you try to mix, just in
case you were thinking of doing so.

I think similar highly confusing scenarios arise when considering whether the
"this" pointer is near or far in mixed memory model programming between small data
and large data models, and I have seen bugs in earlier versions of BC++ in connection 
with this.

I realise I may be fragmenting this thread of argument somewhat, but I would be
interested if anyone out there knows a bit more about this aspect of C++ programming
on PCs.

|> Huge pointers are frought with problems, and you need to know what
|> you're doing in order to use them properly.
|> 
|> -- 
|> #ifdef TRUE        | Fuzzy Fox (a.k.a. David DeSimone)       fuzzy@netcom.com
|> #define  TRUE   0  |
|> #define  FALSE  1  |     "History doesn't repeat itself, but it rhymes."
|> #endif             |                                   -- Mark Twain

All of my opinions are mine
--- Charles Reindorf