Razionale su boost.preprocessore con macro invece di semplici definisce?

Question

Ad esempio BOOST_PP_ITERATE e BOOST_PP_ITERATION, come visto su AnswerSers Qui , sono macro preprocessore, senza parametri.C'è una ragione per cui non sono solo semplici definimenti e usati come tali senza ()?

Answer 1

Generally, function like macro can be used to prevent unintentional macro expansion.
For example, assuming that we have the following macro call:

BOOST_PP_CAT( BOOST_PP_ITERATION, _DEPTH )

and we expect this will be expanded into BOOST_PP_ITERATION_DEPTH.
However, if BOOST_PP_ITERATION is an object like(non-functional) macro, it will be expanded to its own definition before the token BOOST_PP_ITERATION_DEPTH is generated by concatenation.

Answer 2

Presumably because they perform operations: consequently, their usage should make it clear that you are actually invoking something and not just using some constant.