[Bug c++/49679] Increment/decrement operator (++/--) not working as expected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49679

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-07-08 17:57:09 UTC ---
The code has undefined behaviour because there are no sequence points between
the increments, see http://c-faq.com/expr/seqpoints.html

GCC even warns you:

seq.cc: In function 'int main(int, char**)':
seq.cc:19:15: warning: operation on 'a' may be undefined [-Wsequence-point]
seq.cc:19:15: warning: operation on 'a' may be undefined [-Wsequence-point]
seq.cc:20:15: warning: operation on 'b' may be undefined [-Wsequence-point]
seq.cc:20:15: warning: operation on 'b' may be undefined [-Wsequence-point]

You should use -Wall if the compiler seems to be doing something you don't
understand, it might explain why.