Standard C++ Library Reference ISO/IEC (VERSION3)

state-dependent encoding, mbstate_t may actually be unused. So the number of member objects
stored may vary.
fpos::fpos
fpos(streamoff off);
fpos(St state, fpos_t filepos);
The first constructor stores the offset off, relative to the beginning of file and in the initial
conversion state (if that matters). If off is -1, the resulting object represents an invalid stream
position.
The second constructor stores the object state and a file position determined by filepos.
fpos::operator!=
bool operator!=(const fpos& right) const;
The member function returns !(*this == right).
fpos::operator+
fpos operator+(streamoff off) const;
The member function returns fpos(*this) += off.
fpos::operator+=
fpos& operator+=(streamoff off);
The member function adds off to the stored offset member object, then returns *this. For
positioning within a file, the result is generally valid only for binary streams that do not have a
state-dependent encoding.
fpos::operator-
streamoff operator-(const fpos& right) const;
fpos operator-(streamoff off) const;
The first member function returns (streamoff)*this - (streamoff)right. The second
member function returns fpos(*this) -= off.
fpos::operator-=
fpos& operator-=(streamoff off);
The member function returns fpos(*this) -= off. For positioning within a file, the result is
generally valid only for binary streams that do not have a state-dependent encoding.