$PP: The C preprocessor symbol

$PP is shorthand for $UNSTRING($P) (see $P), or (essentially) a synonym for $UNSTRING("#") (see $UNSTRING). It is useful, particularly in FORTRAN, for constructing FWEB macro definitions that expand to C preprocessor statements. For an example, see $P. For a detailed discussion of the difference between $P and $PP, see Strings and quotes.