header file duplicate definitions advice sought

[Stuart Cracraft]

Hello!

I am wondering if someone can help me with a problem I'm trying to resolve.

How can you eliminate redefined errors in C when you have several thousand 
"#define"'s defined in both *.h and *.c files(about 2000 files combined)?

Where *.h and *.c files are scattered around in different directories.

So far I have only collected very few possible ideas to the problem.
One of them is to have "#ifndef" statements over places that I am getting
redefined errors.  However, this is not a good solution because this
will not work on case such as below:

==========================================================================
inside abc.h                          inside def.h
#define a 4                           #define a 5
                 inside ghi.c
		 #include <abc.h>
		 #include <def.h>

            Which value is ghi.c referring to, 4 or 5?
Thus, I would end up searching in ghi.c to see which is a appropriate value
and I might have to do this million times manually for other similar cases.

Another idea is to list all the redefined symbols(using a script to 
retrieve) in following ways:

                    header file      
                     symbol is		
symbol    value       located		files including header files
------    -----     -----------         ----------------------------
a           5        abc.h                def.h
					  xyz.h
					  kuy.c
a	    3	     kby.h		  ubc.h
					  ppp.h

        etc...

This gives me more of general info which I might use it in changing the
symbol name in the header file and also in files where header file
is included.  And I think this is a very clean solution except that
again there are too many symbols(approximately 7000 of them) and I 
would end up spending million years.

I have couple more ideas like above but they are not a good approach.
Actually, I don't think there are any good simple way of resolving 
the problem but I am asking if anyone out there has/had similar 
experience to share with me how you have dealt with the problem.

Thank you (sorry my question got little too lengthy :)