Peter Dalgaard wrote: > > One distinction is if you have things like > > #define f(x) 2*x > #define g(y) f(y+2) > > (in the C language preprocessor syntax), then you end up with g(y) as > y+2*2 (i.e., y+4), whereas the corresponding function calls give > 2*(y+2). Also, and the flip side of the original question: Macros have > difficulties with encapsulation; with a bit of bad luck, arguments > given to f() can modify its internal variables.
using c macros, you end up with g(y) substituted by 2*y+2, rather than y+2*2, as you say (and rather than 2*(y+2), which you'd effectively get using a function). that's why you'd typically include all occurences of all macro 'parameters' in the macro 'body' in parentheses: #define f(x) 2*(x) some consider using c macros as not-so-good practice and favour inline functions. but macros are not always bad; in scheme, for example, you have a hygienic macro system which let's you use the benefits of macros while avoiding some of the risks. vQ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
