How do I log several variables with log4cpp at once?

Question

How do I log more than a single string with log4cpp?

E.g. if I want to log all argv's to main:

#include <iostream>
#include <log4cpp/Category.hh>
#include <log4cpp/FileAppender.hh>
#include <log4cpp/PatternLayout.hh>

using namespace std;

int main(int argc, char* argv[]) {
    log4cpp::Appender *appender = new log4cpp::FileAppender("FileAppender","mylog");
    log4cpp::PatternLayout *layout = new log4cpp::PatternLayout();
    layout->setConversionPattern("%d: %p - %m %n");
    log4cpp::Category& category = log4cpp::Category::getInstance("Category");
    appender->setLayout(layout);
    category.setAppender(appender);
    category.setPriority(log4cpp::Priority::INFO); 

    category.info("program started"); // this works fine, I see it in the logfile

    for(int i=0; i<argc; ++i) {
        // next line does not compile:
        category.info("argv["<<i<<"] = '"<<argv[i]<<"'");
    }

    return 0;
}   

the line

category.info("argv["<<i<<"] = '"<<argv[i]<<"'");

does not compile. Obviously the logger does not work as a ostream. What is the log4cpp way to log something like this, preferable at once?

Answer 1

You have two options:

• Use printf-style formatting:

  for (int i = 0; i < argc; ++i)
  {   
      category.info("argv[%d] = '%s'", i, argv[i]);
  }  
  

• Use infoStream():

  for (int i = 0; i < argc; ++i)
  {
      category.infoStream() << "argv[" << i << "] = '" << argv[i] << "'";
  }  
  

I'd go with the latter.