On 8/13/2010 7:52 AM, Lorenzo Caminiti wrote:
Hello all,
I asked this question before but received no answer: Is there any problem in using `BOOST_PP_UNARY()` to check if a token matches a predefined keyword as indicated by the code below?
The following `IS_PUBLIC(token)` macro expands to 1 if `token` is `public`, to 0 otherwise:
#define PUBLIC_public (1) #define IS_PUBLIC(token) BOOST_PP_IS_UNARY(BOOST_PP_CAT(PUBLIC_, token))
IS_PUBLIC(public) // Expand to 1. IS_PUBLIC(abc) // Expand to 0.
This works just fine on both GCC and MSVC. However, `BOOST_PP_UNARY()` is only part of Boost.Preprocessor private API because:
IS_PUBLIC(+) results in undefined behavior. More generally, the result of token-pasting must result in a single (preprocessing) token. So, for example, BOOST_PP_CAT(abc, 123) and BOOST_PP_CAT(+, +) are okay, but BOOST_PP_CAT(abc, 123.0) and BOOST_PP_CAT(+, -) are not. Similarly for what you have above which will work provided everything used as an argument is an identifier (there are no "keywords" to the preprocessor) or a pp-number that doesn't contain any decimal points. Regards, Paul Mensonides