For each type T from the Standard C library,186 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.