How to Define Preprocessor Macros in CMake?

Defining Preprocessor Macros with CMake

In C , preprocessor macros provide a convenient way to define symbolic constants or alter code behavior during compilation. To define a preprocessor macro using CMake, you have two main options:

Method 1: add_compile_definitions (CMake >= 3.12)

With CMake 3.12 and later, you can use the add_compile_definitions command to define preprocessor macros. This approach is more fine-grained than the previous method and allows you to separate compile definitions, include directories, and compiler options.

add_compile_definitions(OPENCV_VERSION=${OpenCV_VERSION})
add_compile_definitions(WITH_OPENCV2)

Method 2: Legacy add_definitions (Deprecated)

Prior to CMake 3.12, the add_definitions command was used to define preprocessor macros:

add_definitions(-DOPENCV_VERSION=${OpenCV_VERSION})
add_definitions(-DWITH_OPENCV2)

Note: The -D prefix is required in the legacy method to indicate a preprocessor definition.

Additional Considerations:

• You can also define preprocessor macros per target using the target_compile_definitions command.
• For more detailed explanations on the available commands for compiler flags, refer to the CMake documentation at: https://cmake.org/cmake/help/latest/command/add_definitions.html

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