Each seek member function begins execution by constructing an object of class sentry. It returns by destroying the sentry object.
pos_type tellp();
Returns: If fail() != false, returns pos_type(-1) to indicate failure. Otherwise, returns rdbuf()->pubseekoff(0, cur, out).
basic_ostream<charT, traits>& seekp(pos_type pos);
Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::out). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
basic_ostream<charT, traits>& seekp(off_type off, ios_base::seekdir dir);
Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).