Can the C preprocessor be used to tell if a file exists?

Question

I have a very large codebase (read: thousands of modules) that has code shared across numerous projects that all run on different operating systems with different C++ compil

Answer 1

So far as I know cpp does not have a directive regarding the existence of a file.

You might be able to accomplish this with a bit of help from the Makefile, if you're using the same make across platforms. You can detect the presence of a file in the Makefile:

foo.o: foo.c
    if [ -f header1.h ]; then CFLAGS+=-DHEADER1_INC

As @Greg Hewgill mentions, you can then make your #includes be conditional:

#ifdef HEADER1_INC
#include 
#endif