Look in the CPP info page that comes with GCC/EGCS, or any good book on
ANSI C. The CPP info is particularly good at explaining the subtle
points.
You will find that #arg in a macro body expands to "arg" (with arg
substituted), and arg1 ## arg2 expands to both substitutions joined
together with no space between them. These are called stringification
and concatenation. There are subtleties about when macros in the
argument strings are expanded, which is why some macros appear to do
nothing but call other macros -- to affect when expansion occurs.
"arg" and arg1/**/arg2 are old-style forms of the same thing. They
don't work with ANSI C, but the new forms don't work with K&R (old) C.
Hence `#ifdef __STDC__' to decide which to use -- that checks for ANSI
C. The rules about when expansion occur are different for these forms.
-- Jamie
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