I think this is a good overview of preprocessor directives:
http://www.cplusplus.com/doc/tutorial/preprocessor/
It can be very difficult to use search engines for some programming topics because they like to ignore certain characters. I find that extremely frustrating and have not discovered a solution after quite a bit of research. I want to be able to search for an exact term rather than some fuzzy results that assume I'm an idiot. Of course idiot mode is a nice option too since I notice typos in my quick search queries quite often, but I don't want it forced on me.