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C code with macros

P: 18
Hi ,all

#define MAX(x,y) ((x)>(y)?(x):(y)
printf("maximum is %d",MAX(++x,++y));

this is a code using macros....
the output for this code is 6
is my answer right...

i hav a little bit confusion whether the maximum will be 6 or 5...
please clear my confusion..

Thanks in advance....
Aug 6 '07 #1
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7 Replies

Expert Mod 5K+
P: 9,197
The macro expands to:
Expand|Select|Wrap|Line Numbers
  1.  ((++x)>(++y)?(++x):(++y)
x and y are altered multiple times before the end of the statement (called a sequence point). Changing a variable more than once within a given sequence point produces indeterminate results.

Therefore, any answer may be expected.
Aug 6 '07 #2

P: 6
Hey max value will increment two times so take a close look at the code by replacing the macro call by its body
Aug 7 '07 #3

P: 18
ok....i will try some more codes with macros..
Aug 7 '07 #4

P: 2
Answer I think is 7.
Because the result i.e ++y will be calculated twice.
Once during the comparision (++x > ++Y) and again during answering.
++x : ++y.
This sort of arguments should not be used in macros, as their answer cant be predicted easily and they may give unexpected results.

Aug 9 '07 #5

Expert Mod 5K+
P: 9,197
Did anyone read my Post#2??
Aug 9 '07 #6

Expert 10K+
P: 11,448
Did anyone read my Post#2??
I did, but I wasn't participating in this thread ;-) You're right though: the OP should
be happy that no daemons flew out of his nose after doing such naughty deeds.

kind regards,

Aug 9 '07 #7

Expert 100+
P: 463
In this case, I think undefined means that no specific/single value can be expected. Are you going to get -23457898 as an answer? Probably not, but if you're expecting 7 you're going to be just as disappointed. What happens is compiler specific and that spells trouble.
Aug 9 '07 #8

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