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

You could have a pre-build step run that generates an include file that contains a list of #defines that represent the names of the files existing in the current directory:

#define EXISTS_FILE1_C
#define EXISTS_FILE1_H
#define EXISTS_FILE2_C

Then, include that file from within your source code, and then your source can test the EXISTS_* defines to see whether a file exists or not.