Alberto Ganesh Barbati wrote:
this post originates from thread "concatenation of power of negative number" in comp.std.c++ (http://tinyurl.com/asn95). Consider this file:
---- #include <boost/preprocessor/cat.hpp> BOOST_PP_CAT(1e, -1) ----
According to Paul Mensonides' reply in the thread, it should be eventually interpreted as
<1e> ## <-> <1>
thus the pp-number "1e" is concatenated with "-" obtaining the pp-number "1e-" and then "1" is appended as a separate token. The final result would thus be "1e- 1" (notice the blank between "-" and "1").
However, if run into Wave, the program above produces the error message:
error: pasting the following two tokens does not give a valid preprocessing token: "e" and "-"
Who's right? I'd agree with Paul Mensonides, because "1e" is a valid pp token which is to be formed before applying the ## operator. But my understanding is quite limited in this area so I commit myself to the Gurus.
Paul is right and Wave is wrong. That's a known issue with Wave, it stems from the fact that Wave currently works on C++ tokens, not pp-tokens as mandated by the Standard. This will be fixed in the future, when I change Wave to operate on pp-tokens, rescanning these into C++ tokens after preprocessing. If you need to preprocess this kind of constructs with Wave, you may want to use the --variadics command line option, allowing concatenation of unrelated tokens. Regards Hartmut