dolog.hh

#pragma once
#include <iostream>
#include <sstream>
#include <syslog.h>

/* This file is intended not to be metronome specific, and is simple example of C++2011
   variadic templates in action.

   The goal is rapid easy to use logging to console & syslog. 

   Usage: 
          string address="localhost";
          infolog("Bound to %s port %d", address, port);
          warnlog("Query took %d milliseconds", 1232.4); // yes, %d
          errlog("Unable to bind to %s: %s", ca.toStringWithPort(), strerr(errno));

   If bool g_console is true, will log to stdout. Will syslog in any case with LOG_INFO,
   LOG_WARNING, LOG_ERR respectively. If g_verbose=false, infolog is a noop.
   More generically, dolog(someiostream, "Hello %s", stream) will log to someiostream

   This will happily print a string to %d! Doesn't do further format processing.
*/

inline void dolog(std::ostream& os, const char*s)
{
  os<<s;
}

template<typename T, typename... Args>
void dolog(std::ostream& os, const char* s, T value, Args... args)
{
  while (*s) {
    if (*s == '%') {
      if (*(s + 1) == '%') {
	++s;
      }
      else {
	os << value;
	s += 2;
	dolog(os, s, args...); 
	return;
      }
    }
    os << *s++;
  }    
}

extern bool g_console;
extern bool g_verbose;

template<typename... Args>
void genlog(int level, const char* s, Args... args)
{
  std::ostringstream str;
  dolog(str, s, args...);
  syslog(level, "%s", str.str().c_str());
  if(g_console) 
    std::cout<<str.str()<<std::endl;
}

template<typename... Args>
void infolog(const char* s, Args... args)
{
  if(g_verbose)
    genlog(LOG_INFO, s, args...);
}

template<typename... Args>
void warnlog(const char* s, Args... args)
{
  genlog(LOG_WARNING, s, args...);
}

template<typename... Args>
void errlog(const char* s, Args... args)
{
  genlog(LOG_ERR, s, args...);
}