CODEWITHSUNDEEP
c++syntaxmacros
user103260
user103260

Reputation: 99

#define doubts...why this behaviour

I have defined the following max macro

#define max(a,b)(a>b?a:b);

Inside the main() I am doing the following

int t,a,b,c,d;

t=max(a,b)+max(c,d);

But the output is not as expected.t shows only the maximum value among a and b. What could be the problem?

Upvotes: 1

Views: 85

Answers (2)

willy
willy

Reputation: 1490

Remove the ;. a #define is just text replacement.

You should also put a and b in parenthesis as a best practice. This one generally won't do much, since comparison operators take precedence over probably anything you might pass in, but say it were:

    #define mul(a, b) (a * b)

and then you say mul(5-3, 10+2) From this you'd expect the output to be 24 (2 * 12), but what actually gets executed is 5-3 * 10+2, and using order of operations, this becomes 5-(3*10)+2, so your answer would end up as -23 instead. If it had been defined as

    #define mul(a, b) ((a) * (b))

You wouldn't have this problem.

Upvotes: 2

Maroun
Maroun

Reputation: 95968

This will be like writing:

t = (a>b?a:b);+(a>b?a:b);

(Check the preprocessor output)

Remove the ; from the define.

Upvotes: 5

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