Wacek Kusnierczyk wrote:
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).
Oops. Yes. I suppose I had x*2 there at some point....
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
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907
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