#if vs #ifdef

[Rob Browning]

The GNU Coding Standards suggest always #defining a symbol to a value
and using #if tests rather than either defining or not defining that
symbol and using #ifdef or #ifndef.  i.e. instead of "#define FOO",
use "#define FOO 1", and use "#define FOO 0" rather than not defining
it at all.

One reason for this recommendation is that they then encourage you to
write code like this:

  if (SCM_HAVE_ARRAYS)
    {
      ...

rather than using #if/#ifdef/etc. at all.  Their argument is that all
reasonable compilers will generate the same code either way, and using
C code rather than the preprocessor can substantially improve the
readability of the code and allow the C compiler to do more thorough
analysis of all code paths.

Thoughts?  Since I just added new public defines, this seems a good
time to ask.

Thanks

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
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