On Static Linking - Could not instantiate class [org.apache.log4j.ConsoleAppender]

[Unnikrishnan Udinoor <uu...@Brocade.COM>]

Hi,

I am using log4cxx 0.9.7 version. On dynamically linking to the log4cxx
library my C++ application works fine with the logging.
On changing the linking to static log4cxx , I get errors stating that
unable to instantiate the class.

Can someone help me to fix this issue ? Thanks a lot in Advance.

To be specific, this is the error I am getting.

	Could not instantiate class [org.apache.log4j.ConsoleAppender].
	Class 'org.apache.log4j.ConsoleAppender' not found
	Could not instantiate appender named "stdout".


	Could not instantiate class
[org.apache.log4j.RollingFileAppender].
	Class 'org.apache.log4j.RollingFileAppender' not found
	Could not instantiate appender named "R".


My log4j.proerties file is as follows:

	### direct log messages to stdout ###
	log4j.appender.stdout=org.apache.log4j.ConsoleAppender 
	log4j.appender.stdout.Target=System.out 
	log4j.appender.stdout.layout=org.apache.log4j.PatternLayout 
	log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} [%t]
%-5p %c{1}:%L - %m%n

	log4j.appender.R=org.apache.log4j.RollingFileAppender
	log4j.appender.R.File=app.log

	log4j.appender.R.MaxFileSize=100KB
	# Keep one backup file
	log4j.appender.R.MaxBackupIndex=1

	log4j.appender.R.layout=org.apache.log4j.PatternLayout
	log4j.appender.R.layout.ConversionPattern=%d{ABSOLUTE} [%t] %-5p
%c{1}:%L - %m%n

	log4j.rootLogger=trace, stdout,R

Re: On Static Linking - Could not instantiate class [org.apache.log4j.ConsoleAppender]

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

On Nov 28, 2007, at 2:07 PM, Unnikrishnan Udinoor wrote:

> Hi,
>
> I am using log4cxx 0.9.7 version. On dynamically linking to the  
> log4cxx library my C++ application works fine with the logging.
>
> On changing the linking to static log4cxx , I get errors stating  
> that unable to instantiate the class.
>
> Can someone help me to fix this issue ? Thanks a lot in Advance.
>
> To be specific, this is the error I am getting.
>

Use of log4cxx 0.9.7 is discouraged.  Please consider moving to the  
SVN HEAD.  I remember a lot of pain with using log4cxx 0.9.7 from a  
static library and those issues should be fixed in the SVN HEAD.

The issue is due to the class registration information is only linked  
in when there is some explicit reference to the appender in the code.   
In this case, the linker did not see any reference to ConsoleAppender  
or RollingFileAppender when it linked your app, so those object files  
weren't linked into your app.  Since they weren't linked the static  
constructor that adds those classes to the list of available classes  
and so you get the class not found messages.  If you really want to  
use 0.9.7, you need to compel the linker to bring the appenders and  
layouts that you need into the app.  You could do that by having  
something (even unreachable code) in your app call  
ConsoleAppender::getStaticClass(), etc.