The C++ standard library reserves the following kinds of names:
names with external linkage
In namespace std, the following names are reserved for previous standardization:
Each name declared as an object with external linkage in a header is reserved to the implementation to designate that library object with external linkage,177 both in namespace std and in the global namespace.
Each global function signature declared with external linkage in a header is reserved to the implementation to designate that function signature with external linkage.178
Each function signature from the C standard library declared with external linkage is reserved to the implementation for use as a function signature with both extern "C" and extern "C++" linkage,179 or as a name of namespace scope in the global namespace.
The function signatures declared in <cuchar>, <cwchar>, and <cwctype> are always reserved, notwithstanding the restrictions imposed in subclause 4.5.1 of Amendment 1 to the C Standard for these headers.
For each type T from the C standard library,180 the types ::T and std::T are reserved to the implementation and, when defined, ::T shall be identical to std::T.
These types are clock_t, div_t, FILE, fpos_t, lconv, ldiv_t, mbstate_t, ptrdiff_t, sig_atomic_t, size_t, time_t, tm, va_list, wctrans_t, wctype_t, and wint_t.