[xml] singularity in using C++ exceptions with libxml2 library

[Nathan Myers <ncm-xml cantrip org>]

Stanislav Ievlev <inger altlinux org>
> libxml2 needs rebuild with '-fexceptions' to avoid problems with
> exceptions catching.
>
> Attached program is a test to this problem.
>
> With libxml compilled without "-fexceptions" this program cannot catch
> exception from aborter() function

You cannot safely throw a C++ exception out of a callback called 
from C code unless the C library involved was specifically designed
to allow it.  It doesn't matter what compiler flags you use. 
(Also note, it's generally very difficult to allow it and typically
not practical.)

You have to catch the exception in the callback, pass status back 
up the line (in this case by telling the SAX parser to stop parsing, 
and setting some private field in your parse context) and then
returning normally.

Sorry, but that's the way it is.

Nathan Myers