title: configure log4cplus to log to custom file at runtime
body: <p>I am using configuration file to initialize log4cplus module. We use the below command in configuration file to specify the log file name to be generated.</p>
  
  <p><em>log4cplus.appender.log1.File=TestFile.log</em></p>
  
  <p>I want this TestFile.log to be generated at run time. I used setProperty function to change log file name at run time but didn't get the desired result.</p>
  
  <p>In code - </p>
  
  <p><em>log4cplus::helpers::Properties props;
  props.setProperty(LOG4CPLUS_TEXT("File"), LOG4CPLUS_TEXT("TestFile.log"));</em></p>
  
  <p>In configuration file - </p>
  
  <p><em>log4cplus.appender.afile2.File=${File}</em></p>
  
  <p>But this will generate log file as "${File}" instead of "TestFile.log".</p>