I found a thread here
but didn't quite understand it.
I'm trying to do the following.
The installer is set up for several clients. Most of the files are in a general directory. A few, if they are necessary are in a client specific directory. Some clients may need these specific files, others not. A !define tells the compiler which client the installer is being written for.
What I would like to do is, at compile time, if a file exists in a client specific directory, use it, otherwise get the file from a general directory.