README.md

Logger

This is a small, self-contained C++ logger with minimal overhead.

Description

It allows logging messages with different severities, and allows the user of the services to choose which severity they want displayed. This is a niche alternative to Google (glog), spdlog, plog and Boost::Log. It is also compatible with ETL's etl::string. Assuming etl::string<SIZE> text = "Hello", you can use text.data() or text.c_str(). It is lite enough to be used in a microcontroller. It is used for all logging purposes in the AcubeSAT nanosatellite project (and aboard it, with some modifications).

Table of Contents

Click to expand

• Logger
  • Description
  • Table of Contents
  • Usage
  • Features
  • Log Levels
  • Caveats
  • Building

Usage

The logger uses #defines that allow logging through operator<<:

LOG_ERROR << "Fingolfin stumbled backwards into a pit!";
LOG_INFO << "Amon Sûl was struck by " << 42 << " thunderbolts today";
LOG_DEBUG << "Slayed Uruk-Hai " << urukHaiName << " with " << getWeapon(adventurerName);

Don't forget to include the line add_compile_definitions<LOG_LEVEL> in your CmakeLists.txt, for example add_compile_definitions(LOGLEVEL_TRACE).

Features

• Easy-to-customize log levels
• Determine if the level is sufficient for an expression to be logged at compile time
• Empty log entries/log entries that will not be displayed are not processed or stored
• Logs composed with operator<<
• Force inline, to force const propagation; works like a macro in -O1
• Dummy log entry to nuke away vtables, etc.
• ETL-agnostic
• Minimal assembly produced

Log Levels

The following log levels are supported:

Level	Description
trace	Very detailed information, useful for tracking the individual steps of an operation
debug	General debugging information
info	Noteworthy or periodical events
notice	Uncommon but expected events
warning	Unexpected events that do not compromise the operability of a function
error	Unexpected failure of an operation
emergency	Unexpected failure that renders the entire system unusable
disabled	Use this log level to disable logging entirely. No message should be logged as disabled. Must be enforced by the user

Changing the log levels and their order is very simple. In Logger.hpp, change the #defines for the levels, e.g.:

#if defined LOGLEVEL_TRACE
#define LOGLEVEL Logger::trace
#elif defined LOGLEVEL_DEBUG
#define LOGLEVEL Logger::debug

#define LOG_TRACE     (LOG<Logger::trace>())
#define LOG_DEBUG     (LOG<Logger::debug>())

and the enum for the order:

enum LogLevel : LogLevelType {
	trace = 32,
	debug = 64,
	info = 96,
	notice = 128,
	warning = 160,
	error = 192,
	emergency = 254,
	disabled = 255,
};

Caveats

For messages that will not be logged, any calls to functions that contain side effects will still take place:

LOG_DEBUG << "The temperature is: " << getTemperature();

Here, if getTemperature() will cause a side effect (e.g. a std::cout print), it will still be executed, even if the debug message will not be printed to the screen due to an insufficient LOGLEVEL. You should prefer to use functions that return plain values as parts of the log function, so that they might be optimzied away at compile time.

For type casts, etl::to_string and co are your friends. Or, you can just implement the corresponding operators for other types.

Building

If you use this as a standalone, you'll need ETL. You can add it with conan, or as a submodule, etc. To add ETL through conan, there's already a conanfile.txt in the root directory. You can:

• mkdir build && cd build
• conan install ..

1. You might need to run conan profile new default --detect and conan profile update settings.compiler.libcxx=libstdc++11 default, to generate default profile detecting GCC, set old ABI and set libcxx to the C++11 ABI, respectively. This is done to manage the GCC >= 5 ABI
2. After you've run conan install, a conanbuildinfo.cmake file will have been generated. You can then edit the CMakeLists.txt to add the lines include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake) and conan_basic_setup()