text: #include "logger.h"
  
  int main() {
      std::string filename = "./example_log.log";
      SimpleLogger* ll = new SimpleLogger(filename);
      ll->start();
  
      // 0: System  [====]
      // 1: Fatal   [FATL]
      // 2: Error   [ERRO]
      // 3: Warning [WARN]
      // 4: Info    [INFO]
      // 5: Debug   [DEBG]
      // 6: Trace   [TRAC]
  
      // << set log level >>
      // -1: disable
      //  0: upto System
      //  1: upto Fatal
      //  2: upto Error
      //  3: upto Warning
      //  4: upto Info
      //  5: upto Debug
      //  6: upto Trace (all)
      ll->setLogLevel(6);
      ll->setDispLevel(6);
  
      // printf() style.
      _log_fatal(ll, "fatal error");
      _log_err(ll, "error");
      _log_warn(ll, "warning");
      _log_info(ll, "info");
      _log_debug(ll, "debug");
      _log_trace(ll, "trace");
      _log_trace(ll, "parameters %d %d %s", 1, 2, "3");
  
      ll->stop();
      ll->start();
  
      // stream style.
      _s_fatal(ll) << "fatal error";
      _s_err(ll) << "error";
      _s_warn(ll) << "warning";
      _s_info(ll) << "info";
      _s_debug(ll) << "debug";
      _s_trace(ll) << "trace";
      _s_trace(ll) << "multi" << std::endl << "lines " << 123;
  
      delete ll;
      SimpleLogger::shutdown();
  
      return 0;
  }
  