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POVariable length arguments in log4cxx LOG4CXX_ macros
 

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    <p>I am using log4cxx in a big C++ project but I really don't like how log4cxx handles multiple variables when logging:</p> <p>LOG4CXX_DEBUG(logger, "test " &lt;&lt; var1 &lt;&lt; " and " &lt;&lt; var3 " and .....)</p> <p>I prefer using printf like variable length arguments:</p> <p>LOG4CXX_DEBUG(logger, "test %d and %d", var1, var3)</p> <p>So I implemented this small wrapper on top of log4cxx</p> <pre><code>#include &lt;string.h&gt; #include &lt;stdio.h&gt; #include &lt;stdarg.h&gt; #include &lt;log4cxx/logger.h&gt; #include "log4cxx/basicconfigurator.h" const char * log_format(const char *fmt, ...); #define MYLOG_TRACE(logger, fmt, ...) LOG4CXX_TRACE(logger, log_format(fmt, ## __VA_ARGS__)) #define MYLOG_DEBUG(logger, fmt, ...) LOG4CXX_DEBUG(logger, log_format(fmt, ## __VA_ARGS__)) #define MYLOG_INFO(logger, fmt, ...) LOG4CXX_INFO(logger, log_format(fmt, ## __VA_ARGS__)) #define MYLOG_WARN(logger, fmt, ...) LOG4CXX_WARN(logger, log_format(fmt, ## __VA_ARGS__)) #define MYLOG_ERROR(logger, fmt, ...) LOG4CXX_ERROR(logger, log_format(fmt, ## __VA_ARGS__)) #define MYLOG_FATAL(logger, fmt, ...) LOG4CXX_FATAL(logger, log_format(fmt, ## __VA_ARGS__)) static log4cxx::LoggerPtr logger(log4cxx::Logger::getRootLogger()); int main(int argc, char **argv) { log4cxx::BasicConfigurator::configure(); MYLOG_INFO(logger, "Start "); MYLOG_WARN(logger, "In running this in %d threads safe?", 1000); MYLOG_INFO(logger, "End "); return 0; } const char *log_format(const char *fmt, ...) { va_list va; static char formatted[1024]; va_start(va, fmt); vsnprintf(formatted, 1024, fmt, va); va_end(va); return formatted; } </code></pre> <p>And this works perfectly but I know using that static variable (formatted) can become problematic if I start using threads and each thread logging to the same place.</p> <p>I am no expert in log4cxx so I was wondering if the LOG4CXX macros are handling concurrent thread access automatically? or do I have to implement some sort of locking around the log_format method? something that I wan't to avoid due to performance implications.</p> <p>To compile and test this program (in Ubuntu) use :</p> <pre><code>g++ -o loggertest loggertest.cpp -llog4cxx </code></pre>
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    1. COThank you. Found this topic rather useful. I agree with the comments to use std::string instead, even thought it might have a greater impact on performance. Guess the major factor is that logic becomes cleaner in this case.
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