类
<ios> <iostream>
std::is_error_code_enum (io_errc)
template <>struct is_error_code_enum<io_errc> : public true_type {};error_code enum flag for io_errc
This traits specializations identifies io_errc as an error code enum type. Enabling it to be used to construct or assign values of this type to objects of type error_code.
For io_errc it inherits from true_type.