Mike Long <mikel@shore.net> said:
> Multiple inclusion protection does not keep cpp from reading the whole
> header each time it is #included. 

This is just a SMOP.  Nothing prevents the compiler from noticing when a
file consists entirely of comments, blank lines, and lines that are
wrapped in a single #if or #ifdef block, keeping a record of the relevant
#if or #ifdef conditions, testing those conditions when you try to
#include the same file again, and deciding not to bother opening the file
at all if the conditions are such that including the file would not be
useful. 

--apb (Alan Barrett)