2015 Update:
If you need more flexibility, custom formatting, writing your own loggins sinks, etc then you should try out g3log.
G3log is the successor of g2log. G3log can be found at

2016 Update:
Please note that for Windows you need VS 2013 or newer.
Ref: VS 2012


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

Conditional logging
int less = 1; int more = 2
LOG_IF(INFO, (less<more)) <<"If the condition was 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);

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/MSVC and Ubuntu/gcc/clang.

  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

  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
    G3log is the recommended logger in the "g2log-g3log" family.
    G2log is kept alive here at bitbucket due to a demand for a logger in an environent where
    the latest compiler support for C++11 and newer is available.


2013, Sept 24th
* Added support for Clang. Tested on Linux, not OSX.

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 gcc or some fairly recent version of clang.

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


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 ..

--- Building on Linux/Clang ----

cd g2log
mkdir build_clang
cd build_clang
cmake -DCMAKE_CXX_COMPILER=clang++ ..

--- 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

-- Test the test exectutable with

(windows) Release\g2log-FATAL.exe 
or (Linux) ./g2log-FATAL


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 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


It gives me a boost to know that people and companies out there use g2log. If you use it
feel free to drop me a line.

If you like it (or not) it would be nice with some feedback. That way I can
improve g2log. 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 :)

Kjell (a.k.a. KjellKod)