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Update CMake build documentation
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Dean Moldovan
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@ -26,146 +26,28 @@ Building with cppimport
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Building with CMake
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===================
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For C++ codebases that already have an existing CMake-based build system, the
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following snippet should be a good starting point to create bindings across
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platforms. It assumes that the code is located in a file named
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:file:`example.cpp`, and that the pybind11 repository is located in a
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subdirectory named :file:`pybind11`.
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For C++ codebases that have an existing CMake-based build system, a Python
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extension module can be created with just a few lines of code:
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.. code-block:: cmake
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cmake_minimum_required(VERSION 2.8)
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cmake_minimum_required(VERSION 2.8.12)
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project(example)
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# Add a CMake parameter for choosing a desired Python version
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set(EXAMPLE_PYTHON_VERSION "" CACHE STRING
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"Python version to use for compiling the example library")
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add_subdirectory(pybind11)
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pybind11_add_module(example example.cpp)
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include(CheckCXXCompilerFlag)
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This assumes that the pybind11 repository is located in a subdirectory named
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:file:`pybind11` and that the code is located in a file named :file:`example.cpp`.
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The CMake command ``add_subdirectory`` will import a function with the signature
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``pybind11_add_module(<name> source1 [source2 ...])``. It will take care of all
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the details needed to build a Python extension module on any platform.
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# Set a default build configuration if none is specified.
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# 'MinSizeRel' produces the smallest binaries
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if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
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message(STATUS "Setting build type to 'MinSizeRel' as none was specified.")
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set(CMAKE_BUILD_TYPE MinSizeRel CACHE STRING "Choose the type of build." FORCE)
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set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "Debug" "Release"
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"MinSizeRel" "RelWithDebInfo")
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endif()
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string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE)
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The target Python version can be selected by setting the ``PYBIND11_PYTHON_VERSION``
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variable before adding the pybind11 subdirectory. Alternatively, an exact Python
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installation can be specified by setting ``PYTHON_EXECUTABLE``.
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# Try to autodetect Python (can be overridden manually if needed)
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set(Python_ADDITIONAL_VERSIONS 3.4 3.5 3.6 3.7)
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if (NOT ${EXAMPLE_PYTHON_VERSION} STREQUAL "")
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find_package(PythonLibs ${EXAMPLE_PYTHON_VERSION} EXACT)
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if (NOT PYTHONLIBS_FOUND)
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find_package(PythonLibs ${EXAMPLE_PYTHON_VERSION} REQUIRED)
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endif()
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else()
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find_package(PythonLibs REQUIRED)
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endif()
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A working sample project, including a way to invoke CMake from :file:`setup.py` for
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PyPI integration, can be found in the [cmake_example]_ repository.
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# The above sometimes returns version numbers like "3.4.3+";
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# the "+" must be removed for the next lines to work
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string(REPLACE "+" "" PYTHONLIBS_VERSION_STRING "+${PYTHONLIBS_VERSION_STRING}")
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# Uncomment the following line if you will also require a matching Python interpreter
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# find_package(PythonInterp ${PYTHONLIBS_VERSION_STRING} EXACT REQUIRED)
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if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU")
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CHECK_CXX_COMPILER_FLAG("-std=c++14" HAS_CPP14_FLAG)
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CHECK_CXX_COMPILER_FLAG("-std=c++11" HAS_CPP11_FLAG)
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if (HAS_CPP14_FLAG)
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set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
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elseif (HAS_CPP11_FLAG)
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set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
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else()
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message(FATAL_ERROR "Unsupported compiler -- at least C++11 support is needed!")
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endif()
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# Enable link time optimization and set the default symbol
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# visibility to hidden (very important to obtain small binaries)
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if (NOT ${U_CMAKE_BUILD_TYPE} MATCHES DEBUG)
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# Default symbol visibility
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set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility=hidden")
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# Check for Link Time Optimization support
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CHECK_CXX_COMPILER_FLAG("-flto" HAS_LTO_FLAG)
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if (HAS_LTO_FLAG)
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set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto")
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endif()
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endif()
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endif()
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# Include path for Python header files
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include_directories(${PYTHON_INCLUDE_DIR})
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# Include path for pybind11 header files -- this may need to be
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# changed depending on your setup
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include_directories(${PROJECT_SOURCE_DIR}/pybind11/include)
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# Create the binding library
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add_library(example SHARED
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example.cpp
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# ... extra files go here ...
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)
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# Don't add a 'lib' prefix to the shared library
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set_target_properties(example PROPERTIES PREFIX "")
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if (WIN32)
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if (MSVC)
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# /MP enables multithreaded builds (relevant when there are many files), /bigobj is
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# needed for bigger binding projects due to the limit to 64k addressable sections
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set_property(TARGET example APPEND PROPERTY COMPILE_OPTIONS /MP /bigobj)
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# Enforce size-based optimization and link time code generation on MSVC
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# (~30% smaller binaries in experiments); do nothing in debug mode.
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set_property(TARGET example APPEND PROPERTY COMPILE_OPTIONS
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"$<$<CONFIG:Release>:/Os>" "$<$<CONFIG:Release>:/GL>"
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"$<$<CONFIG:MinSizeRel>:/Os>" "$<$<CONFIG:MinSizeRel>:/GL>"
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"$<$<CONFIG:RelWithDebInfo>:/Os>" "$<$<CONFIG:RelWithDebInfo>:/GL>"
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)
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set_property(TARGET example APPEND_STRING PROPERTY LINK_FLAGS_RELEASE "/LTCG ")
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set_property(TARGET example APPEND_STRING PROPERTY LINK_FLAGS_MINSIZEREL "/LTCG ")
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set_property(TARGET example APPEND_STRING PROPERTY LINK_FLAGS_RELWITHDEBINFO "/LTCG ")
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endif()
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# .PYD file extension on Windows
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set_target_properties(example PROPERTIES SUFFIX ".pyd")
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# Link against the Python shared library
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target_link_libraries(example ${PYTHON_LIBRARY})
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elseif (UNIX)
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# It's quite common to have multiple copies of the same Python version
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# installed on one's system. E.g.: one copy from the OS and another copy
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# that's statically linked into an application like Blender or Maya.
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# If we link our plugin library against the OS Python here and import it
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# into Blender or Maya later on, this will cause segfaults when multiple
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# conflicting Python instances are active at the same time (even when they
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# are of the same version).
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# Windows is not affected by this issue since it handles DLL imports
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# differently. The solution for Linux and Mac OS is simple: we just don't
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# link against the Python library. The resulting shared library will have
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# missing symbols, but that's perfectly fine -- they will be resolved at
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# import time.
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# .SO file extension on Linux/Mac OS
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set_target_properties(example PROPERTIES SUFFIX ".so")
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# Strip unnecessary sections of the binary on Linux/Mac OS
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if(APPLE)
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set_target_properties(example PROPERTIES MACOSX_RPATH ".")
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set_target_properties(example PROPERTIES LINK_FLAGS "-undefined dynamic_lookup ")
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if (NOT ${U_CMAKE_BUILD_TYPE} MATCHES DEBUG)
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add_custom_command(TARGET example POST_BUILD
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COMMAND strip -u -r ${PROJECT_BINARY_DIR}/example.so)
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endif()
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else()
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if (NOT ${U_CMAKE_BUILD_TYPE} MATCHES DEBUG)
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add_custom_command(TARGET example POST_BUILD
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COMMAND strip ${PROJECT_BINARY_DIR}/example.so)
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endif()
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endif()
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endif()
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.. [cmake_example] https://github.com/dean0x7d/pybind11_cmake_example
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