The current C++ standard is ISO/IEC 14882:2014 (C++14). The standard, which describes the core language and the standard libraries, must be bought from ANSI, ISO, or the BSI. Here we present the available draft, and thus free, versions of the standard.
Available C++ Standard Drafts and Related Documents
There are some drafts for C++98, the first ISO C++ standard, but they are not from the WG21 site.
C++98 [ISO/IEC 14882:1998(E)] - From www.kuzbass.ru (local) there a document called 'Final Draft', dated May 1998. A PDF version is available from plumber.gnu-darwin.org (local), dated September 1998. There is also a Proposed Defect Report on ISO/IEC1488:1998 (local) from WG21.
There is a good language reference that covers C++11 and C++14 features at cppreference.com.
Standard Template Library Programmer's Guide documents all of the components in the SGI Standard Template Library and provides other more general STL resources
Frank B. Brokken's C++ Annotations is a general C++ tutorial.