Did you ever want to print logging messages to console for debugging, and wished it was color-coded? Of course, there are numerous full-fledged logging libraries out there that can do the task. But sometimes the effort of including them for a small project is just too much!

Enter fclog - short for Formmatted Console LOGger - a wrapper around good old std::cout that prints color-coded debug messages to the terminal. Light enough to work on an embedded platform (well, one that supports C++ with iostream) like my friendly Onion Omega 2+

Download the two files, fclog.h and fclog.cpp, add them to your C++ project, and you're all set.

In your code initialize fclog like so:

  // This is the declaration -> void Logger(fclog::Severity min_severity = fclog::Severity::INFO, bool print_timestamp = false);
  fclog::Logger(/*min_severity = */fclog::Severity::NOTICE, /*print_timestamp = */true);

and then use the appropriate log function where needed...

  using namespace fclog; // -> use the functions without typing the namespace prefix everytime
  ...
  DEBUG() << "this is a" << " debug message" << std::endl;
  INFO() << "this is an" << std::endl << " informational message" << std::endl;
  ...
  int result = system("echo 'My Main Man'");
  ERROR_IF(result != 0) << "echo failed : this is a catastrophe!" << std::endl;

As seen from the declaration in fclog.h,

  void Logger(fclog::Severity min_severity = fclog::Severity::INFO, bool print_timestamp = false);

fclog takes two configuration inputs at initialization:

1. Minimum log severity level (default: INFO) - an enum
2. Whether to print timestamp to console (default: false) - a boolean

Just pass in the values you want, or nothing if you're happy with the defaults.

Simply put, fclog is a C-style wrapper around C++ functions (Blasphemy! I know!). Log severity levels are defined in an enum in the header file, fclog.h. The entire logic is implemented in a single "static" function called logItem. The declared functions INFO(), DEBUG(), ERROR(), etc. --and their *_IF(...) variants-- simply call logItem with appropriate prefixes and color codes to print.

In lieu of a class or struct, two (2) static "state variables" are used in fclog.cpp:

• short min_log_level - keeps track of the minimum log severity level chosen at initialization; messages are printed to console if the enum value is lower than min_log_level (check the function, doLog() and its usage for clarity);
• bool disp_time - keeps track of whether to print a timestamp to the console; if true the timestamp is formatted as std::put_time( /*std::tm*/&utm, "%F %T %Z " ) and printed to console.

A third static variable,

• ostream cnull(0) - represents a null output stream: it acts like dev/null and is used to bypass printing to console;

If you're looking to log to files, or want a full-fledged solution with file rotation etc., one of the following will be better for your application
(in no particular order):

• ulog
• plog
• spdlog - I've used spdlog in other C++ (commercial) projects and it's fantastic!
• loguru
• NanoLog

Currently, this module seems complete. I'm happy to receive feedback on code correctness and optimization. Also, if you have alternative suggestions, please share them.