3B2 cpp #ifdef + #include

[Karl Heuer]

In article <3127 at csli.STANFORD.EDU> gandalf at csli.stanford.edu (Juergen Wagner) writes:
>The problem with your cpp is that all the lines starting with # have to
>be valid syntax, i.e. "junk junk" is not relevant because it is just text
>and cpp doesn't know if this is correct or not, but "# include junk" is
>invalid because is violates cpp syntax.

"#include junk" is legal (in ANSI C, anyway) if "junk" is a macro that expands
into a quoted or embroketed header name.  Thus,
  #ifdef junk
  #include junk
  #endif
should be legal.  This is indeed a bug in certain preprocessors.  Similarly, I
believe that the warning produced by
  #ifdef vms
  #ifdef foo$bar /* a valid name, in VMS */
  #endif
  #endif
on non-VMS systems is inappropriate, though I haven't yet determined what the
latest dpANS says about this.

Karl W. Z. Heuer (ima!haddock!karl or karl at haddock.isc.com), The Walking Lint
Followups to comp.lang.c only.