MAP_NEXT0 parameter list, changing the output. Ifĭoing that forms a macro call, everything moves over by a slot in the This macro works by placing the item next to the MAP_GET_END macro. #define MAP_NEXT(item, next) MAP_NEXT1 (MAP_GET_END item, next) #define MAP_NEXT1(item, next) MAP_NEXT0 (item, next, 0) Parameter if the item is anything else: #define MAP_GET_END() 0, MAP_END The macro returns MAP_END if the item matches, or the next Macro compares a single list item against the special end-of-list marker To actually select between the two macros, the following MAP_NEXT Recursive macro when the time comes to quit: #define MAP_END(.)Įvaluating this macro does nothing, which ends the recursion. The basic idea is to emit the following macro name instead of the normal The next challenge is to stop the recursion when it reaches the end of the This provides the basic framework for recursion, at least within a Produce 365 copies of the word blah, followed by a final un-evaluated B (blah). In other words, calling EVAL (A (blah)) would #define EVAL(.) EVAL4 (EVAL4 (EVAL4 (_VA_ARGS_)))Įach level multiplies the effort of the level before, evaluating the inputģ65 times in total. Its arguments down a tree of macro calls: #define EVAL0(.) _VA_ARGS_
To perform these repeated evaluations, the following EVAL macro passes The recursion continues as long as the callerĬontinues to feed the output text back into the preprocessor. Feeding this text back into the preprocessor expands the call,Įvaluating the output a third time expands the A (blah) macro, carrying Just plain text at this point, and B isn't even the name of the current The preprocessor doesn't see any recursion, since the B (blah) call is Imagine we have the following macros: #define A(x) x B MAP_OUT (x)Įvaluating the macro A (blah) produces the output text: blah B (blah) MAP(PRINT, a, b, c) /* Apply PRINT to a, b, and c */įirst, we need a technique for emitting something that looks like a macro The end goal is to create a MAP macro which works like this: #define PRINT(a) printf(#a": %d", a) If you found any error or any queries related to the above program or any questions or reviews, you wanna to ask from us ,you may Contact Us through our contact Page or you can also comment below in the comment section.We will try our best to reach upto you in the short interval.Yes, recursive macros are possible in C using a fancy workaround.
0 kommentar(er)
