g2log-dev is hereby retired but know that its purpose was well achievied. g2log-dev helped as feature playground for [g3log]. I will keep g2log-dev repo as is since there are several people out there who is still using it.

My recommendation is to switch to g3log which has better performance, is easier to customize and is the main g2log-branch that will continue to grow and be maintained.

My best KjellKod

Original Introduction below


Optional to use either streaming or printf-like syntax LOG(INFO) << "As Easy as ABC or " << 123; or LOGF(WARNING, "Printf-style syntax is also %s", "available");

Conditional logging int less = 1; int more = 2 LOG_IF(INFO, (less<more)) <<"If [true], then this text will be logged";

// or with printf-like syntax
LOGF_IF(INFO, (less<more), "if %d<%d then this text will be logged", less,more);

Design-by-Contract CHECK(false) will trigger a "fatal" message. It will be logged, and then the application will exit.

CHECK(less != more); // not FATAL
CHECK(less > more) << "CHECK(false) triggers a FATAL message");


In depth information can be found at

Or just read the short summary below:

G2log is an asynchronous, "crash safe" logger and design-by-contract library. What this means in practice is that

  1. All the slow I/O disk access is done in a background thread. This ensures that the other parts of the software can immediately continue with their work after making a log entry.

  2. g2log provides logging, Design-by-Contract [#CHECK], and flush of log to file at shutdown. Buffered logs will be written to file before the application shuts down.

  3. It is thread safe, so using it from multiple threads is completely fine.

  4. It is CRAsH SAFE, in that it will catch certain fatal signals, so if your application crashes due to, say a segmentation fault, SIGSEGV, or some other fatal signals it will log and save to file this crash and all previously buffered log entries before exiting.

  5. It is cross platform. For now, tested on Windows7 and Ubuntu

  6. On Ubuntu a caught fatal signal will generate a stack dump to the log. This is not yet available on Windows due to the platforms complexity when traversing the stack. Stack dump on Windows will be released later and a beta is available on request.

  7. G2log is used in commercial products as well as hobby projects since early 2011. The code is given for free as public domain. This gives the option to change, use, and do whatever with it, no strings attached.

  8. The stable version of g2log is available at The in-development g2log where new features are tried out is available at ongoing and released features can be
    seen at


2012, Oct 14th Complete threadsafe use of localtime for timestamp. (see code: g2time) Runtime change of filename, request of filename. (see code g2logwoker g2future) * Tested on x86 Windows7: Visual Studio 2012 Desktop Express x86 Ubuntu 11.04: gcc 4.7.3 x64 Ubuntu 12...: gcc 4.7.2 x64 Windows7: Visual Studio 2012 Professional

NOTE: It does NOT work with "Visual Studio 11 Beta" (not as C++11 compliant as VS2012)


This g2log is a snapshot from KjellKod repository. It contains what is needed to build example, unit test and performance test of g2log.

justthread C++11 thread library is no longer needed. On Windows it is enough to use Visual Studio 11 (2012). On Linux it is enough to use gcc4.7.2.

The CMakeFile.txt is updated to reflect that, the justthread parts is commented away in case someone still needs that.

If you want to integrate g2log in your own software you need the files under g2log/src


The default is to build an example binary 'g2log-FATAL' I suggest you start with that, run it and view the created log also.

If you are interested in the performance or unit tests then you can enable the creation of them in the g2log/CMakeLists.txt file. See that file for more details

--- Building on Linux --- cd g2log mkdir build cd build cmake .. make

--- Building on Windows --- Please use the Visual Studio 11 (2012) command prompt "Developer command prompt" cd g2log mkdir build cd build cmake -DCMAKE_BUILD_TYPE=Release -G "Visual Studio 11" .. msbuild g2log_by_kjellkod.sln /p:Configuration=Release Release\g2log-FATAL.exe


3rdParty -- gtest, glog.

gtest is needed for the unit tests. glog is only needed if you want to run the glog vs g2log comparison tests

gtest is enabled as a DEFAULT option in the CmakeFiles.txt file. If the unit test is not important for you then just DISABLE that option. By default the gtest zipped library must be UNPACKED before it is used (compilation)

gtest It IS included by the CMake and you don't need to do install or compile it in any other way than through the g2log cmake setup.

Google's glog is not included and must be installed ONLY IF you want to run the comparison tests

About the A ctive Object

Is made with standard C++ components with the help of the latest C++11 and std::thread features (thanks to justthread). For more details see

An example is provided. Other examples on pre C++0x Active Objects can also be found at (code page)

If you like it (or not) it would be nice with some feedback. That way I can improve g2log and it is also nice to see if someone is using it. If you have ANY questions or problems please do not hesitate in contacting me on my blog or at <Hedstrom at KjellKod dot cc>

Good luck :)

Cheers Kjell (a.k.a. KjellKod)