C preprocessor: documentation and use outside of the C compiler

[Doug Gwyn <gwyn>]

> Is there any documentation anywhere about the C preprocessor, or does
> one need to read through the source code to find out how to use it
> outside of the C compiler?

The UNIX System V User Reference Manual documents the C preprocessor
under CPP(1).  It also warns you that the C preprocessor is intended
only for use via "cc" with C sources and that any other use may
break some day.  I assume this refers to the possibility of bundling
the CPP functions into the lexical analyzer where they belong.