Custom appender (was Re: Building log4cxx 0.9.7 with MinGW and MSYS (no cygwin))

Was this related to MinGW thread?  I didn't appear to be so I've 
changed the subject.
First, let me warn you that there are major changes forthcoming in the 
CVS that will significantly impact appenders.  I hope to have those 
committed in the CVS within the week.
Without more details on the nature of the appender that you are 
writing, it is hard to give any concrete suggestions.  I assume that it 
is not something that would be general purpose that would be good to 
discuss openly and have added to log4cxx.  If so, it would be better to 
discuss it before getting down to implementation details.
Probably the best approach is to take ConsoleAppender (which derives 
from WriterAppender) and start modifying it to include any needed 
configuration.
On your LayoutPtr question, I you are trying to call 
WriterAppender(LayoutPtr&, ostream*).  Most appenders do have 
non-default constructors, but they are only used in unusual 
circumstances.  In general, logging is configured from a configuration 
file which will use the default constructor, call setOption to 
configure the appender, then call activateOptions to get things ready 
for use.  The likely best approach is to defer constructing your 
ostream until the activateOptions method and then set the 
WriterAppender::os variable.
As for your actual question, it is trivial to create a LayoutPtr;

log4cxx::LayoutPtr layout;  // initialized as a reference to null

or

log4cxx::LayoutPtr layout(new log4cxx::PatternLayout("%m %n\n"));


The implementation of appenders is intentionally similar to log4j.  You 
may find it easier to do an initial implementation and experimentation 
on log4j and then port your appender to log4cxx.