bsl::basic_stringbuf::seekoff

Set the current input position or the current output position (or both) to the specified offset from the specified whence location. Optionally specify a modeBitMask indicating whether to set the current input position, current output position, or both. If whence is ios_base::beg, set the current position to the indicated offset from the beginning of the stream; if whence is ios_base::end, set the current position to the indicated offset from the end of the stream; and if whence is ios_base::cur, set the current input or output position to the indicated offset from its current position. If whence is ios_base::cur, then modeBitMask may be either ios_base::in or ios_base::out, but not both. Return the offset of the new position on success, and pos_type(off_type(‐1)) otherwise.