Re: Does log4cxx support variable-arguments?

On Sep 17, 2006, at 1:58 PM, sishen wrote:

> Hey. everyone.
>
> I'm a new user of log4cxx. I want to know whether log4cxx support  
> variable argument?
> I have found the maillist archive, but i haven't got any answers.
>
> for example, like the macro:
> #define  LOG4CXX_DEBUG(logger, message)
>
> it only takes two argument.  And now i have to combine all argument  
> to a string.
>
> This is not convenient. I think variable-argument is common for  
> logging system.
> Any advice prefer, :)


No, however the message parameter can be an expression, the  
expression could be a function that takes varargs or has multiple  
signatures.  The expression is only evaluated if the threshold is  
satisified, so if you do something like:

LOG4CXX_INFO(logger, logfmt("%s %s %d", arg1, arg2, arg3));

The logfmt method would only be called if logger's threshold level is  
INFO or above (where logfmt would be a method you defined that  
returned std::string or std::wstring).  The LOG4CXX_INFO are  
preprocessor macros which handle all the details in passing the  
caller information to the actual logger methods.  If they were not  
preprocessor macros the __LINE__ and __FILE__ would refer the the  
location of the method implementation, not the caller.  As  
preprocessor macros, they do not have the ability to overload the  
macro name with multiple definitions for different argument lists.