static long bitalloc();
The ios class currently defines 15 format flag bits accessible through flags and other member functions. These bits reside in a 32-bit private ios data member and are accessed through enumerators such as ios::left and ios::hex.
The bitalloc member function provides a mask for a previously unused bit in the data member. Once you obtain the mask, you can use it to set or test the corresponding custom flag bit in conjunction with the ios member functions and manipulators listed below under “See Also.”
ios::flags, ios::setf, ios::unsetf, ios setiosflags manipulator, ios resetiosflags manipulator