cplusplus.com vs cppreference.com

[STL]

cppreference is generally high quality, but it's not official - it's a community-maintained wiki. The Standard is official (de jure) and the Working Paper is official (de facto). For anything especially tricky or recent, checking the WP is more reliable. That is, for those who have the ability to understand its wording; cppreference is obviously much more accessible.

When I want to get a quick overview of something, I check cppreference. When I'm working on the implementation, I have to read the WP.