C Preprocessor Abuse
The C Preprocessor can be used to do many very interesting and amusing things.
String Constant Inclusions
Suppose you want to include the entirety of the file "foo" as a string literal. This actually has the potential to be useful in some circumstances, like for storing templates in a shared library. Note that this only works if the file being included ends with a closing paren [that's a ), by-the-by] which is not a part of the final file, and that, in the resultant literal, all whitespace will be collapsed.