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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