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Using OpenSpiel as a C++ Library

OpenSpiel has been designed as a framework: a suite of games, algorithms, and tools for research in reinforcement learning and search in games. However, there are situations where one may only want or need a single game/algorithm or small subset from this collection, or a research experiment does not require modifying or otherwise interacting very closely with OpenSpiel other than strictly calling/using it.

In cases like this, it might be nice to use OpenSpiel as a library rather than a framework. This has the benefit of not forcing the use of certain tools like CMake or having to continually recompile OpenSpiel when doing your research.

Luckily, this is easy to achieve with OpenSpiel: you simply need to build it as a shared library once, and then load it dynamically at runtime. This page walks through how to do this assuming a bash shell on Linux, but is very similar on MacOS or for other shells.

Compiling OpenSpiel as a Shared Library

To build OpenSpiel as a shared library, simply run:

mkdir build
cd build
BUILD_SHARED_LIB=ON CXX=clang++ cmake -DPython3_EXECUTABLE=$(which python3) -DCMAKE_CXX_COMPILER=${CXX} ../open_spiel
make -j$(nproc) open_spiel

This produces a dynamically-linked library libopen_spiel.so (or lib_openspiel.dylib on MacOS) in build/ that can be linked against and loaded dynamically at run-time.

Suppose OpenSpiel was installed in $HOME/open_spiel. The following line adds the necessary environment variable to let the shell know where to find libopen_spiel.so at run-time:

export LD_LIBRARY_PATH="${HOME}/open_spiel/build"

You might want to add this line to your $HOME/.bash_profile to avoid having to do it every time you load the library. Of course, if you are already using LD_LIBRARY_PATH for something else, then you need to add ${HOME}/open_spiel/build to it (space-separated paths).

Compiling and Running the Example

cd ../open_spiel/examples
clang++ -I${HOME}/open_spiel -I${HOME}/open_spiel/open_spiel/abseil-cpp \
        -L${HOME}/open_spiel/build -lopen_spiel -std=c++17 \
        -o shared_library_example shared_library_example.cc

The first two flags are the include directory paths and the third is the link directory path. The -lopen_spiel instructs the linker to link against the OpenSpiel shared library.

That's it! Now you can run the example using:

./shared_library_example breakthrough

You should also be able to register new games externally without the implementation being within OpenSpiel nor built into the shared library, though we are always interested in growing the library and recommend you contact us about contributing any new games to the suite.