fstream obj(filename , ios::in);
obj.seekp(7);

fstream obj(filename , ios::in);
obj.seekg(7);

basic_ostream<charT,traits>& seekp(pos_type pos);

pos_type seekpos(pos_type sp,
ios_base::openmode which = ios_base::in | ios_base::out);

basic_istream<charT,traits>& seekg(pos_type pos);