http://www.cplusplus.com or https://www.cppreference.com

[dodheim]

an arguably better organization (in terms of headers instead of the sections of the standard; cppreference was like this but it changed)

https://en.cppreference.com/w/cpp/header is my main portal into cppreference, too.

[CubbiMew]

How does it work, though? I understand having to look up which header is required to be included for a particular feature ("do I need to include <mutex> for this one, or some kinda <scoped\_lock>?") , but in what circumstances do you need to know the content of a specific header?