Re: Does log4cxx support variable-arguments?

I've defined my own logging macros that use <sstream>, for example:

> #include <sstream>
>
> // define logging macros using streams
> #define LOG_LOG(_logger_, _level_, _message_) { \
>         if (_logger_->isEnabledFor(_level_)) {\
>         ::std::stringstream sstr;\
>         sstr << _message_;\
>         _logger_->forcedLog(_level_, sstr.str(), LOG4CXX_LOCATION); } }
>
> #define LOG_DEBUG(_logger_, _message_)  LOG_LOG(_logger_, 
> ::log4cxx::Level::DEBUG, _message_)
> #define LOG_ERROR(_logger_, _message_)  LOG_LOG(_logger_, 
> ::log4cxx::Level::ERROR, _message_)

I can then use something like this:

LOG_ERROR("something nasty happened: status=" << status << ", value=" << 
value);

This has the effect of allowing multiple arguments (although in fact the 
whole expression is a single macro argument).
Additionally, it allows easy use of objects ostream methods, to allow 
them to describe their own state/value.

Hope this helps,

Derek


Curt Arnold wrote:
> 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.

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