[ebuddington@mail.wesleyan.edu: cccp.c::print_help() not called.]

[Zack Weinberg]

On Sun, Apr 02, 2000 at 01:53:01AM -0500, Eric R. Buddington wrote:
> On Sat, 1 Apr 2000, Zack Weinberg wrote:
> 
> > There is no -u option; you must mean -undef.  Except that that doesn't
> > do what it's documented to do...
> > 
> > $ /work/inst/bin/cpp -undef -dM /dev/null
> > #define __i386__ 1
> > #define __tune_pentiumpro__ 1
> > #define i386 1
> > #define __i386 1
> 
> Probably not important at this point, but my cpp recognizes a -u option,
> which does something useful:
...
> bash-2.02$ cpp -u -dM /dev/null
> # 1 "/dev/null"

Yeah, but it doesn't do what you think it does.  Watch:

$ cpp --version
2.95.2
$ cpp -dM /dev/null -u
cpp: argument to `-u' is missing

You thought it was undefining symbols because the -dM got eaten, so it
didn't print anything - but you would never have seen `# 1 "/dev/null"'
in -dM mode.

It turns out that -u is passed to the linker.  From man ld:

       -u sym Forces sym to be entered in the output file as an
              undefined symbol.  This may, for example, trigger
              linking of additional modules from standard libraries.
              -u may be repeated with different option arguments to
              enter additional undefined symbols.

And no, the 'cpp' wrapper won't ever run the linker, but it recognizes
the option anyway.

zw