c - Macro result malfunction in an operation -


this question has answer here:

i tried macro:

#define min(x,y) x<y? x:y

it's supposed return minimum , does. problem when trying use result of macro in operation, doesn't work.

example

x=min(3,4);

here x naturally have 3 value, when trying this:

x= 23 + min(3,4);

the result still 3 (the result of macro), no matter number add (23 arbitrary in there). may know why happens?

the problem operator assocativity , precedence. when expand macro, becomes:

x = 23 + 3 < 4 ? 3 : 4;

which interpreted as:

x = (23 + 3) < 4 ? 3 : 4;

because arithmetic has higher precedence comparison operators. should wrap expansion in parentheses force treated single expression.

#define min(x,y) (x<y? x:y)

you should put parenthese around uses of each parameter, in case they're expressions operators have lower precedence <.

#define min(x,y) ( (x) < (y) ? (x) : (y) )

demo

but using macro function still bad idea. repetitions of parameters mean can't use expressions side effects. e.g. min(i++, j++) increment 1 of variables twice. better use inline function.


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