Some Obscure C Features
This was c++ and not C, but it is a preprocessor pitfall.<p>I needed to compare and older and newer version of some file from the RCS, so I saved temporary copies named "new" and "old". diff told me what I needed to know, but I failed to delete those temp files.<p>Hours later I typed "make" to build my program and got all sorts of errors deeply nested in some library function.  Did someone misconfigure the server I was on?  OK, maybe it is an incremental build problem? etc.  It took took long to figure out the problem.<p>It turns out that during compilation, as one of the library .h files was being scanned, it contained #include <new>, which picked up the junk file in my working directory instead of using the C library.