A C++ logger library for multi-threads realtime system.
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C++ logger library for multi-threads realtime system with printf like format.

Your code





Work in progress

Work in progress. Important changes may happen. (Doc may be not UpToDate)


I've done literally no profiling / performance test so far!! This is evil! I will (and have to) do it soon! I will also check the actual performance with several threads logging concurrently. For now, my solution could be even slower than simple cout.



This project is a C++ logger designed for realtime softwares. In this case, realtime doesn't actual mean that logs are displayed in realtime. Instead, my goal is that logging shouldn't affect the programme execution time. (The least we can). Inside the software thread (Your running programme), logs call only queue the message. The logger is started on its own thread which then process the logs, print them, write in files etc...


  • Simple logging calls with log levels
    • LOG_WTF
    • LOG_INFO
  • Printf like log format
    • Log message works like printf message format.
    • Log max size is 255 char (Truncated if higher).
  • Outputs
    • Write logs in several outputs.
      • File
      • Cout
      • Visual Studio Console (Cout is not supported)
    • Define your own IOutput implementation.
  • Channels
    • Up to 10 channels (ID from 0 to 9)
    • Each channel may be binded to several outputs.
      • Use default configuration for fast use.
      • Set manually outputs in the channels.
  • Log configurations
    • Log Level: Bypass all logs with lower critique level.
    • Save: save all logs in safe files.
    • Reset log files at start (Except saved logs).

Use the library in your project


  • Build the logger library (Or download the build if available).
  • Add elephant include path in your project includes path.
  • Add static library in your project dependencies.
  • Add #include <elephantlogger/log.h> into your cpp/h files.
  • Call elephant::initDefault() in your main.
  • Log things with LOG_X macro (Change X with log level).
  • You're done!

Setup channels and outputs

You may either use the default settings or use your custom settings.

Default Outputs

Simply use elephantlogger::initDefault() at the beginning of your program. This is usually done in the main function.

#include <elephantlogger/log.h>
int main(int argc, char** argc) {
    // Your code
    return 0;

Default settings is the following:

  • Channel 0
    • Logs in Cout console.
    • Logs in File in TMP folder, with name "elephant-cout.log".
  • Channel 1
    • Logs in VS console.
    • Logs in File in TMP folder, with name "elephant-vs.log".
  • Channel 2
    • Logs in just one file, in TMP folder, with name "elephant.log"

Custom Outputs

You may want to manually set outputs to a specific channel (Up to 10). The steps to follow:

  • Include the Output header.
  • Create static Output variable.
  • Initialize the logger with init() (Instead of initDefault).
  • Add each output in the channel you want.

WARNING: It is actually important to respect this order! (Otherwise, static variable would be destroyed while logger still use them).


// Include Output headers
#include "elephantlogger/outputs/ConsoleCout.h"
#include "elephantlogger/outputs/ConsoleVS.h"
#include "elephantlogger/outputs/LogFile.h"

#include <elephantlogger/log.h>

int main(int argc, char** argc) {
    static elephantlogger::ConsoleCout  coutConsole;
    static elephantlogger::ConsoleVS    visualConsole;
    static elephantlogger::LogFile      logFile("/path/to/log/folder/"   "filename.log");
    static elephantlogger::LogFile      logFileVS("/path/to/log/folder/" "filename.log");


    elephantlogger::addOutput(0, &coutConsole);   // Channel 0 logs on cout
    elephantlogger::addOutput(1, &visualConsole); // Channel 1 logs on VS
    elephantlogger::addOutput(2, &logFile);       // Channel 2 logs in file
    elephantlogger::addOutput(1, &logFileVS);     // Channel 1 also log in file

    // Your code
    return 0;

Build the library

Dependencies / Requirements

  • C++11
  • experimental/filesystem support (stdc++fs)
  • thread (pthread)
  • pragma support (pragma once)

Build on GNU/Linux with CMake

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
make -j4

DCMAKE_BUILD_TYPE options: Debug / Release / RelWithDebInfo / MinSizeRel

Build on GNU/Linux from command line

g++ -I/path/to/elephant/include/ yourProject.cpp /paht/to/libelephantlogger.a -pthread -lstc++fs

You may add -g -Wall for debug.

Execute examples on GNU/Linux with CMake

Set CMake option "BUILD_EXAMPLES" to ON (OFF by default)

mkdir build
cd build
make -j4
make ex1

DCMAKE_BUILD_TYPE options: Debug / Release / RelWithDebInfo / MinSizeRel

Start example 1. For other, change '1' by example number.

Build on Windows

TODO: Not supported yet.

API Reference overview

All end-user function are accessible through elephantlogger namespace and are all listed in include/elephantlogger/log.h header.

For further details, see exact function documentation from the log.h header or in doxygen doc.

Log macros

Probably what you will use the most

  • LOG_WTF(channelID, msg) Log something that should never happen (For strange behavior etc)
  • LOG_ERROR(channelID, msg) Log an error.
  • LOG_WARNING(channelID, msg) Log a warning.
  • LOG_CONFIG(channelID, msg) Log a configuration.
  • LOG_INFO(channelID, msg) Log an information.
  • LOG_TRACE(channelID, msg) Log a trace information.
  • LOG_DEBUG(channelID, msg) Log a debug.

Settings and other functions

  • init() Initialize the logger.
  • initDefault() Initialize the logger with default parameters.
  • saveLogs(where) Save all current logs in a safe place.
  • addOutput(channelID, channelPtr) Add an output for a specific channel.
  • setLogLevel(level) Change the used log level.
  • getTmpFilePath() Get the temporary folder path (May change on each OS).
  • log(...) Log something (You won't call it directly, use log macros instead).


Several examples are available in examples directory.

#include "elephantlogger/log.h"

#include <chrono>
#include <thread>

// A simple test
int main(int argc, char** argv) {

    elephantlogger::initDefault(); // Init and set default outputs.

    LOG_WTF(0, "Log wtf (For things that should never happen!)");
    LOG_ERROR(0, "Log an error");
    LOG_WARNING(0, "Warning");
    LOG_CONFIG(0, "Some configuration");
    LOG_INFO(0, "Some information");
    LOG_TRACE(0, "Trace information");
    LOG_DEBUG(0, "The famouse debug!");

    LOG_DEBUG(0, "Integer value: %d", 42);
    LOG_DEBUG(0, "Float value: %f", 31.9);
    LOG_DEBUG(0, "Bool value (true): %d", true);
    LOG_DEBUG(0, "NULL (Using d): %d", NULL);
    LOG_DEBUG(0, "NULL (Using s): %s", NULL);

    LOG_DEBUG(0, "String: %s / Integer: %d / Float: %f / Char: %c", "Hello", 2, 7.1, 'c');

    for(int k = 0; k < 4; ++k) {
        LOG_DEBUG(0, "Log in loop (counter: %d)", k);

    LOG_INFO(0, "See you");
    return 0;

Generate Doxygen documentation

  • doxygen Doxyfile
  • Documentation generated in build-doxygen folder.


See the github issues-section

Beware with the format in logs. In case of wrong format (Ex: %s instead of %d), you may have weird errors without nice warning information. (It may even be a segfault error.)