Custom Appender

[Yusuf Cinar <ci...@yahoo.com>]

Hi

I am trying to write a custom appender following VectorAppender, 
here http://svn.apache.org/viewvc/logging/log4cxx/trunk/src/test/cpp/vectorappender.h?view=co, as
 an example.

However, I am getting an error when calling my custom Appenders constructor:

undefined reference to `log4cxx::VirtualAppender::VirtualAppender()' -- see 
below in red.

I am not sure what is going on but guessing that I am not linking a library 
although I am linking log4cxx.a, apr-1.a, aprutil-1.a, xml2.a, expat.a. Is there 
another library to link when creating a Custom appender inherited 
from AppenderSkeleton?

Below is the code snippet.

Thanks in advance for any help.

#ifndef VIRTUALAPPENDER_H_
#define VIRTUALAPPENDER_H_

#include <log4cxx/appenderskeleton.h>
#include <log4cxx/spi/loggingevent.h>

namespace log4cxx
{
class VirtualAppender : public AppenderSkeleton
{
    public:
  DECLARE_LOG4CXX_OBJECT(VirtualAppender)
              BEGIN_LOG4CXX_CAST_MAP()
                      LOG4CXX_CAST_ENTRY(VirtualAppender)
                      LOG4CXX_CAST_ENTRY_CHAIN(AppenderSkeleton)
              END_LOG4CXX_CAST_MAP()

              VirtualAppender();
              ~VirtualAppender();

                /**
                This method is called by the AppenderSkeleton#doAppend
                method.
                */
                void append(const spi::LoggingEventPtr& event, 
log4cxx::helpers::Pool& p)
                {
                LogString test =  event->getMessage();
                }

                void close();

                bool isClosed() const
                        { return closed; }

                bool requiresLayout() const
                        { return false;   }
};

}

#endif /* VIRTUALAPPENDER_H_ */

My app:

#include <iostream>
using namespace std;

// include log4cxx header files.
#include "log4cxx/logger.h"
#include "log4cxx/basicconfigurator.h"
#include "log4cxx/helpers/exception.h"
#include "VirtualAppender.h"

using namespace log4cxx;
using namespace log4cxx::helpers;

LoggerPtr logger(Logger::getLogger("MyApp"));

int main() {
cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!

    VirtualAppender * vAppender = new VirtualAppender(); // Error happens here
    logger->addAppender(vAppender);
    LOG4CXX_INFO(logger, "Entering application.");
    LOG4CXX_INFO(logger, "Exiting application.");

return 0;
}



      

Re: Custom Appender

[Curt Arnold <ca...@apache.org>]

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.