Predefined Compiler Identifiers/Variables

[James L Strickland]

I have run across references to predefined names/identifiers/symbols
associated with C compilers.  These appear to be things such as:
unix, vax, MSDOS, etc..., depending on the compiler.

How are these identifiers implemented on a UNIX box?  Are they
part of the compiler or in a file that is used at compile time?
How can I find out the value of the predefined identifiers for
our system?

-- 
James Strickland - Systems Programmer  jstrickland at dsac.dla.mil
Defense Logistics Agency Systems Automation Center (DSAC)
Office of Information System Facilities, AIS Software Division,
Distributed Systems (FSD)  (614) 238-9649  AV 850-9649