It is an attempt to create simple, readable, flexible and universal logger for personal purposes. The main idea is implement useful tool, which can be easy added to any C++ project.

First ideas, which were implemented here, were come up and developed in the SQL to CypherQL Converter.

1. How to use
2. Appenders
   1. FileAppender
   2. ConsoleAppender
3. Formatters
   1. TXTFormatter
   2. FuncMessagesFormatter
   3. OnlyMessagesFormatter
   4. JSONFormatter
4. Inspired by
5. License

Now, you can download this repository and manually integrate Logger into your project.

• Add logger/include to the project include paths;
• Import logger/log.hpp, where you want to use Logger;
• Import header with special initializer like file_appender_initializer.hpp to init the logger (only once);
• Write your first log:

  #include "logger/log.hpp"
  #include "logger/initializers/file_appender_initializer.hpp"
  
  int main() {
      logger::init(logger::info, "../log");
  
      LOG(logger::info) << "Hello, world!";
      LOGI << "Short form";
      
      return 0;
  }

• Read logs in the 2022-09-25-22:26:16.log file:

  2022-09-25 22:26:16 [INFO] main.cpp main() at line 7: Hello, world!
  2022-09-25 22:26:16 [INFO] main.cpp main() at line 8: Short form
  

This tools contains a lot of macros. You can choose any (See file log.hpp).

The most important and "root" macros are LOG(severity) and LOG_IF(condition, severity).

The same table of macros, but with condition:

You can write logs in the several places at the same time. Just add new appender to the logger instance:

logger::init(logger::debug, "../log");
logger::init(logger::error, logger::cerr);

LOGF << "fatal error";

Log "fatal error" will be written in the file inside the ../log directory and in the cerr stream too.

Notice: if you set different severity levels to appenders, you will have logs in the output stream according to message's severity and severity of each appender.

logger::init(logger::debug, "../log");
logger::init(logger::error, logger::cerr);

LOGE << "Something went wrong!"; // will be written in both
// ...
LOGD << "try to open file...";   // will be written only in the file
open(file);

This appender writes logs in the special .log file, path of which was specified during logger::init call.

When you invoke logger::init(), you pass path to the log's directory or to the desired regular file as the second argument. This path is processed by internal functions and as result new folder for the logs will be created.

New folder path will be according to this table:

This appender writes logs in the console stream (stdout or stderr), which was specified during logger::init call. Logs recorded with the ConsoleAppender have special colours according to the Severity level.

You can colour every message with special severity as you want. Just use method set_console_colour in the Logger class:

void set_console_colour(Severity severity, const MessageColours& msg_cols);

where MessageColours is a struct, which consist of two colours: for the text and its background.

struct MessageColours {
    Colour text;
    Colour bg;
};

Also, you can turn coloured output off, just use the following methods:

void turn_colours_on();
void turn_colours_off();

logger::Logger::get()->set_console_colour(logger::info,
                                          {logger::yellow, logger::common});

where logger::common equals to "without colour" (transparent background or common text colour).

Each formatter is a class, which has special static method format:

static std::string format(const Record& r);

The Formatters can represent log records in different forms.

When you use init function to initializing the logger this formatter is set by default. Log messages represents in the following format:

2022-09-25 22:26:16 [INFO] main.cpp main() at line 11: Hello, world!

as you can see, there are timestamp, severity, file, function, line and message.

This formatter contains only message with the function, which sent it, and line.

main.cpp@11: Hello, world!

You can use this formatter, if you want see only the log messages.

Hello, world!

This formatter represents logs as json array:

[
	{
		"timestamp":"2023-02-17T12:46:31.237Z",
		"severity":"FATAL",
		"file":"main.cpp",
		"function":"main",
		"line":"9",
		"message":"Fatal"
	},
	{
		"timestamp":"2023-02-17T12:46:31.237Z",
		"severity":"ERROR",
		"file":"main.cpp",
		"function":"main",
		"line":"10",
		"message":"Error"
	}
]

Some ideas of implementation was inspired by PLOG project, which is more complicated and thoughtful for now :)

This project is licensed under the MIT license. You can freely use Logger in your commercial or opensource software.