Re: C-Ada Import of struct's -- Help

[emery@goldfinger.mitre.org (David Emery)]

I'm sorry, but Bob Wells' techniques are not very reliable/portable,
and will fail on many Ada compilers.

Bob makes the significant mistake of assuming that an Ada access type
has any relation to an address.  This is not a valid assumption on
some Ada compilers.  

Even when an access type is an address, it doesn't necessarily point
to the right thing.  By Definition in C, a "char *" representing a string
is the address of the first element of the string.  There's no
guarantee that an Ada access type points to the first element of the
string.  In fact, there is significant existing practice where the
access type points to a 'descriptor', which contains the address of
the first element of the string.  

The same reasoning holds true, even more so, for the other array type.  

Also, don't forget that a C string must be null-terminated.  Ada
provides no such guarantee for its strings.

In my (long and painful) experience interfacing Ada and C, I've found
that the right approach is to bend over backwards and provide C with 
the exact thing it asks for (e.g. the address of the first element of
a string is represented in Ada by STR(STR'FIRST)'ADDRESS).
Fortunately, we can use the features of Ada to hide this ugliness
within a package body, protecting the innocence of the programmer
using the package...

				dave
--
--The preceeding opinions do not necessarily reflect the opinions of
--The MITRE Corporation or its sponsors. 
-- "A good plan violently executed -NOW- is better than a perfect plan
--  next week"                                      George Patton
-- "Any damn fool can write a plan.  It's the execution that gets you
--  all screwed up"                              James Hollingsworth
-------------------------------------------------------------------------