you don't need much C++ knowledge at all to start coding, PMB might confirm this from his own experience. Some C knowledge is needed anyway. but as always, it's better to know more about something before you start using it on some other topic
learning C++ is rather a matter of years than a matter of weeks. Of course you go thru a c++ book within a few days , but in my opinion you might know the features of C++ then, but how to use them in a reasonable way is quite another issue, since C++ gives you such a lot of freedom that it's often not easy to decide which way to go. but that comes automatically while coding different stuff.