ios_base flags

ios_base flags to the C Mode flags mapping: in->"r", out or out|trunc->"w", out|app->"a",in|out->"r+",in|out|trunc->"w+"

Reference: C++ Standard Library, The: A Tutorial and Reference, MobiPocket by Nicolai M. Josuttis. Addison-Wesley, 1999, p. 632.