First. it would be best for you to define your custom appenders in a namespace
other than log4cxx.
Second, you declare a constructor, destructor and close method for
VirtualAppender, but you did not provide an implementation. Unless you
compiled and linked in a file that looked like:
#include "VirtualAppender.h"
log4cxx::VirtualAppender::VirtualAppender() {
}
log4cxx::VirtualAppender::~VirtualAppender() {
}
void log4cxx::VirtualAppender::close() {
}
Then the linker would be expected to complain that there was no implementation
provided.
