libstdc++-6-doc 6.5.0-2ubuntu1~18.04 (amd64 binary) in ubuntu bionic

 This package contains documentation files for the GNU stdc++ library.
 .
 One set is the distribution documentation, the other set is the
 source documentation including a namespace list, class hierarchy,
 alphabetical list, compound list, file list, namespace members,
 compound members and file members.