------- Comment #2 from _deepfire at feelingofgreen dot ru 2008-02-23 11:56 ------- > I think this is correct CPP behavior. > it only evaluates one level of _ .
Interesting, reading the CPP manual[1] gives me an impression that there is at least intent to support nested expansions: > You might wonder, “Why mention the prescan, if it makes no difference? > And why not skip it and make the preprocessor faster?” The answer is > that the prescan does make a difference in three special cases: > > * Nested calls to a macro. > > We say that nested calls to a macro occur when a macro's argument > contains a call to that very macro. For example, if f is a macro that expects > one argument, f (f (1)) is a nested pair of calls to f. The desired expansion > is made by expanding f (1) and substituting that into the definition of f. > The prescan causes the expected result to happen. Without the prescan, f (1) > itself would be substituted as an argument, and the inner use of f would > appear during the main scan as an indirect self-reference and would not be > expanded. But in my case the nesting is not immediately observable, and therefore requires further body expansion to detect and apply that strategy. I wonder what will be the final call of GCC people on that -- will this use pattern be considered legit-enough to deserve support, or not. 1. http://gcc.gnu.org/onlinedocs/cpp/Argument-Prescan.html#Argument-Prescan -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35301
