string host_name();
string host_name(error_code& ec);
template<class Allocator>
basic_string<char, char_traits<char>, Allocator>
host_name(const Allocator& a);
template<class Allocator>
basic_string<char, char_traits<char>, Allocator>
host_name(const Allocator& a, error_code& ec);
Returns: The standard host name for the current machine, determined as if by POSIX gethostname.
Remarks: In the last two overloads, ill-formed unless allocator_traits<Allocator>::value_type is char.