c++-font-lock-extra-types is a variable defined in `cc-vars.el'.
Its value is

("\\sw+_t" "FILE" "lconv" "tm" "va_list" "jmp_buf" "istream" "istreambuf" "ostream" "ostreambuf" "ifstream" "ofstream" "fstream" "strstream" "strstreambuf" "istrstream" "ostrstream" "ios" "string" "rope" "list" "slist" "deque" "vector" "bit_vector" "set" "multiset" "map" "multimap" "hash" "hash_set" "hash_multiset" "hash_map" "hash_multimap" "stack" "queue" "priority_queue" "type_info" "iterator" "const_iterator" "reverse_iterator" "const_reverse_iterator" "reference" "const_reference")

*List of extra types (aside from the type keywords) to recognize in C++ mode.
Each list item should be a regexp matching a single identifier.
For example, a value of ("string") means the word "string" is treated
as a type name.

Note that items on this list that don't include any regexp special
characters are automatically optimized using `regexp-opt', so you
should not use `regexp-opt' explicitly to build regexps here.

On decoration level 3 (and higher, where applicable), a method is used
that finds most types and declarations by syntax alone. This variable
is still used as a first step, but other types are recognized
correctly anyway in most cases. Therefore this variable should be
fairly restrictive and not contain patterns that are uncertain.

Note that this variable is only consulted when the major mode is
initialized. If you change it later you have to reinitialize CC Mode
by doing M-x c++-mode.

Despite the name, this variable is not only used for font locking but
also elsewhere in CC Mode to tell types from other identifiers.

You can customize this variable.