Herb Sutter stated, that with the event of C++11 every single line of code in any book written before must be adapted or completely changed.
Translating this to Stack Overflow means, that at least many correct C++ answers are outdated even if they happen to be technically correct.
I think it should be possible to flag an old C++ question where this is the case and it should be possible to flag a new answer as being a C++11 cleanup. Most of the cleanups will of course be just about replacing old with uniform initialization or about replacing
Such flagging may then have many effects. In addition, to allow searching for flagged questions/answers it should be possible to maybe also mask the answers so only up to date answers are visible. Maybe it would be helpful to adapt the reputation system to incentivise flagging and cleanup-answering.
As things are now, users new to C++ will get quite confused with the different styles of writing C++. Many old questions and answers are still often viewed and thus important but completely forgotten by the Stack Overflow community and thus not maintained.
UPDATE I want to raise attention to a c++ specific issue and start a discussion on how old answer threads can be improved. I completely agree with the complainers here that editing an answer itself should only be done in very rare cases, for e.g. if the only thing to do is
I am not even trying to push forward a specific solution. What I would have liked to push through however is to tag this question as c++ specific thereby to restrict the audience.