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Revision as of 13:33, 9 May 2010 by Baoilleach (Talk | contribs) (Building the Python bindings)

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Open Babel trunk (destined to become openbabel-2.3) will use CMake as its primary build system. Cmake is available in many Linux distributions or from

Building OpenBabel

CMake version 2.6.3 or newer is required to build OpenBabel.

The preferred method of building Open Babel with CMake is to use "out of source" builds. This means that no generated files are placed in the source directory. This ensures good separation between source and build files. You can use whatever directory structure you prefer, one possible directory layout is:


So, if you want to build the source code directly from our subversion repository, you would first check out the code as follows:

mkdir ~/src
cd ~/src
svn co openbabel

And to compile the code:

mkdir ~/build
mkdir ~/build/openbabel
cd ~/build/openbabel
cmake -DCMAKE_INSTALL_PREFIX=/usr/local/openbabel ~/src/openbabel
sudo make install

This would configure OpenBabel in the build directory, make all files and install them to the specified prefix. The CMakeCache.txt file contains most stored settings, erasing that will allow you to configure again.

To run the tests, first set BABEL_DATADIR=~/src/openbabel/data and BABEL_LIBDIR=~/build/openbabel/lib. Then run "make test".

Building the Python bindings

To build the Python bindings you need to specify "-DPYTHON_BINDINGS=ON". If you are compiling from the subversion repository, you will need to generate the bindings in the first place with "-DRUN_SWIG=ON" (note: this requires SWIG 1.3.40, which should either be on the PATH or specified with "-DSWIG_EXECUTABLE=/my/path").

The installation directory will be the global site-packages if neither PYTHON_PREFIX nor CMAKE_INSTALL_PREFIX is specified (i.e. "-DPYTHON_PREFIX=/my/path"). If PYTHON_PREFIX is specified, then this will be used to install the bindings. Finally, if CMAKE_INSTALL_PREFIX is specified, but not PYTHON_PREFIX, then PYTHON_PREFIX is set to CMAKE_INSTALL_PREFIX.

Notes for developers

Make Individual Targets

CMake has good dependency tracking, but it uses timestamps (as most build systems do) to indicate a file has changed. As such anytime that the openbabel library is rebuilt all of the plugins/executables that link to it are relinked. This can lead to excessive amounts of time spent waiting for everything to relink, when the ABI has in fact not changed. By making individual parts of the project these relinks can be avoided.

make openbabel       # Rebuild the openbabel libary
make help            # List available build targets

The dependency tracking can also take time when building plugins. CMake adds an additional target that has no dependency tracking, and can be used if working on the CML format for example,

make cmlformat/fast

This can be used for all targets by appending '/fast' to the target name.

Target Naming Conventions

Formats are named after their source files, e.g. cmlformat.[h|cpp] -> cmlformat. The openbabel library target is named openbabel (currently openbabel-2 on Windows). The executable targets are named after the corresponding executable, e.g. babel. Any of these target names can be used as shown above to rebuild specific parts, this can save a lot of time when working on one specific aspect of Open Babel.

Useful Cmake Options

  • To see the actual commands used to compile the code (on Linux), run 'make VERBOSE=1'
  • You can build in debug mode with "-DCMAKE_BUILD_TYPE=Debug".
  • On occasion, developers may find it useful to use the option -DMINIMAL_BUILD=ON. This option just compiles the Smiles and SDF formats, and of the tools just babel.

OpenBabel GUI

The OpenBabel GUI is built by default if the wxWidgets development libraries are available (on Ubuntu 9.04, libwxgtk2.8-dev; Fedora, wxGTK-devel). On Windows, the WXWIN environment variable should be defined.

The GUI build can be explicitly disabled using -DBUILD_GUI=OFF.

Building on Windows

There is a batch file, default_build.bat, in the windows-vc2008 folder that runs cmake. Other .bat files called default_build with additional options, e.g. to enable the tests.