30 Input/output library [input.output]

30.5 Iostreams base classes [iostreams.base]

30.5.3 Class ios_­base [ios.base]

30.5.3.7 ios_­base constructors/destructor [ios.base.cons]

ios_base();
Effects: Each ios_­base member has an indeterminate value after construction.
The object's members shall be initialized by calling basic_­ios​::​init before the object's first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.
~ios_base();
Effects: Destroys an object of class ios_­base.
Calls each registered callback pair (fn, index) ([ios.base.callback]) as (*fn)(​erase_­event, *this, index) at such time that any ios_­base member function called from within fn has well-defined results.