libstdc++/2020: fstream initialization seg-faults if global locale is missing required facets

[bumgard@roguewave.com]

>Number:         2020
>Category:       libstdc++
>Synopsis:       fstream initialization seg-faults if global locale is missing required facets
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Feb 18 16:06:02 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Gregory Bumgardner
>Release:        gcc-3_0-branch
>Organization:
>Environment:
Red Hat Linux 2.2.16
>Description:
Creation of an fstream instance produces a segmentation
fault if the global locale does not contain a ctype facet
matching the template parameters of the filebuf 
instantiation.

A bad_cast exception is thrown by a call to use_facet<> 
in the basic_filebuf constructor, and this causes the
as yet, incomplete fstream instance to be destroyed.

The actual fault appears to occur because the ios_base 
destructor calls ios_base::_M_call_callbacks before the
_M_callbacks field has been initialized. This happens
because basic_ios<>, as a virtual base class, is constructed
before basic_ostream's constructor has called its init()
method. This constructor is never executed because the
bad_cast exception is produced while constructing the
filebuf that would be supplied as its streambuf argument.

This problem might also exist for other stream types.
>How-To-Repeat:
Instantiate a basic_ofstream using a character type other
than char or wchar_t, and construct an instance of that
stream without changing the original global locale.
>Fix:
Not sure. May need to do go ahead and do 
initialization in default constructor.
>Release-Note:
>Audit-Trail:
>Unformatted: