really basic single-header C++ logging for one-off projects

log.h

#ifndef _LOG_H_
#define _LOG_H_

// logging utils
//
#include <iostream>
#include <ctime>

#define LOG(level) ::log_internal::_log_helper<::log_internal::loglevel:: level >(__FILE__, __LINE__, __FUNCTION__)

namespace log_internal {

enum loglevel {
  TRACE=0,
  DEBUG=10,
  INFO=20,
  WARN=30,
  WARNING=30,
  ERROR=40,
};

std::ostream& operator<<(std::ostream& os, loglevel l) {
  switch (l) {
    case TRACE : os << "TRACE"; break;
    case DEBUG : os << "DEBUG"; break;
    case INFO  : os << "INFO";  break;
    case WARN  : os << "WARN";  break;
    case ERROR : os << "ERROR"; break;
    //default    : os.setstate(std::ios_base::failbit);
    default    : os << static_cast<int>(l);
  }
  return os;
}

template<loglevel level>
inline std::ostream& _log_helper(const char* file, int line, const char* function) {
  // log format is defined as below.
  // (note: clog is not tie()'d with cout, so not autoflushed on stdout, for performance)
  thread_local char ts[50];
  std::time_t t = std::time(nullptr);
  size_t res = std::strftime(ts, sizeof(ts), "%F %T", std::localtime(&t)); // ISO 8601 timestamp
  return std::cerr << '[' << (res ? ts : "<strftime failed>") << ' ' << file << ':' << line << ' ' << function << ' ' << level << "] - ";
}

} // namespace log_internal

#endif