POSIX vs SVID

[Doug Gwyn]

From:  Doug Gwyn <gwyn at smoke.brl.mil>

In article <11188 at cs.utexas.edu> From:  Don_Lewine at dgc.ceo.dg.com
>Question: Is there anything wrong with this?  If I write a strictly
>conforming application, can I include <unistd.h> for SVID 
>compatibility even if POSIX does not require it?  Is there any 
>problem with including "extra" header files (other than the obvious 
>restrictions on the namespace)?

Yes, there can be a problem any time an extra header is included,
if there is no guarantee as to the identifiers that the header may
usurp.  No POSIX implementation can require an application to use
any facilities beyond what the POSIX standard requires for the
application, so if in fact UNIX System V were to need the extra
header (which it doesn't), it would not be POSIX compliant.  Note
that the means by which a POSIX-conforming compilation/execution
environment is obtained on your system may be nonobvious..

Volume-Number: Volume 21, Number 32