>>288
そんな保証はない

§21.1.2
2 Requires: For a certain character container type char_type, a related container type INT_T shall be a
type or class which can represent all of the valid characters converted from the corresponding
char_type values, as well as an end-of-file value, eof(). The type int_type represents a character
container type which can hold end-of-file to be used as a return type of the iostream class member
functions.217)
typedef OFF_T off_type;
typedef POS_T pos_type;

§27.1.2
The classes of clause 27 with template arguments charT and traits behave as described if
traits::pos_type and traits::off_type are streampos and streamoff respectively.
Except as noted explicitly below, their behavior when traits::pos_type and traits::off_type
are other types is implementation-defined.