CMAKE_PROJECT_VERSION_MAJOR
The major version of the top level project.
This variable holds the major version of the project as specified in the top level CMakeLists.txt file by a project() command. Please see CMAKE_PROJECT_VERSION documentation for the behavior when multiple project() commands are used in the sources.
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Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.15/variable/CMAKE_PROJECT_VERSION_MAJOR.html