Write a New Custom Logger

To write a new, custom Logger class, you need to do the following:

• define your logger class and write the code that actually emits the log;
• define logger traits to characterize your logger.

A simplistic example (simplified version of Tomographer::Logger::FileLogger) of a logger is given below.

class StderrLogger; // forward declaration
namespace Tomographer { namespace Logger {
  // Traits for StderrLogger
  template<>
  struct LoggerTraits<StderrLogger> : DefaultLoggerTraits
  {
    enum {
      // fprintf is actually thread-safe, so our logger is thread-safe
      IsThreadSafe = 1,
      // set this to a particular level to unconditinally discard any
      // message logged with strictly lower importance level.
      StaticMinimumImportanceLevel = -1
    };
  };
} } // namespaces

class StderrLogger : public Tomographer::Logger::LoggerBase<StderrLogger>
{
public:
  StderrLogger(int level = Logger::INFO)
    : Tomographer::Logger::LoggerBase<StderrLogger>(level)
  {
  }

  // Change the log level
  //
  // WARNING: This method is not thread-safe!
  //
  inline void setLevel(int level)
  {
    // call the protected LoggerBase<StderrLogger>::setLogLevel()
    setLogLevel(level);
  }

  inline void emit_log(int level, const char * origin,
                       const std::string & msg)
  {
    std::string finalmsg;

    if (level == Logger::ERROR) {
      finalmsg = "ERROR: ";
    } else if (level == Logger::WARNING) {
      finalmsg = "Warning: ";
    }
    
    finalmsg += "["+std::string(origin)+"] " + msg;

    // display the log message
    fprintf(fp, "%s\n", finalmsg.c_str());
  }
};