Comma as a Sequence point:How it works

[vickywiz]

plz explain how comma operator is effecting the value of VAL and o/p is showing 11 instead of 22

]#include<stdio.h>
int main()
{
int val;
  (val=11)
 + (val=22,
   printf("VAL = %d\n", val)
    );
return 0;
}

Output:
VAL=11

[leppyr64]

On mine it shows 22. Why do you think this could be? What did you learn from your last question?

prog.c: In function ‘main’:
prog.c:8: warning: operation on ‘val’ may be undefined
prog.c:8: warning: value computed is not used

Interesting? Why is this warning thrown?

[vickywiz]

i compiled d code in gcc 4.4.5....it gave VAL=11...well according to functioning of comma operator 22 should be returned as value of VAL...
source:http://gcc.gnu.org/bugzilla/show_bug.cgi?id=6409..

[leppyr64]

Joseph S. Myers 2002-04-22 10:16:11 UTC
State-Changed-From-To: open->closed
State-Changed-Why: Sequence points define a partial ordering, not a total
ordering. There is no ordering in the example between
(val=11) and any part of the other argument of +. Both
arguments of the comma operator conflict with (val=11),
causing undefined behavior if this code is ever executed
(so the compiler can make deductions on the basis that
it never will be executed).