cmake如何找到包裹？

Question

I am trying to understand how cmake finds packages, using the FindXXX.cmake file. As an example, the library OpenNI has the file FindOpenNI.cmake defined here: https://github.com/PointCloudLibrary/pcl/blob/master/cmake/Modules/FindOpenNI.cmake

Now, at the bottom of that file, there is the following:

if(OPENNI_FOUND)
  # Add the include directories
  set(OPENNI_INCLUDE_DIRS ${OPENNI_INCLUDE_DIR})
  message(STATUS "OpenNI found (include: ${OPENNI_INCLUDE_DIRS}, lib: ${OPENNI_LIBRARY})")
endif(OPENNI_FOUND)

What I do not understand is where the variable OPENNI_FOUND is defined, because this is the first point in the file that it is mentioned.

I would have thought that this file itself is used to find OpenNI, by searching the directories as dictated in the file's contents. However, it seems that OPENNI_FOUND must have been declared before. Therefore, it is confusing to me: FindOpenNI.cmake is being used to find OpenNI, but during that process, it has been given the variable OPENNI_FOUND , which itself tells cmake whether OpenNI has been found.

So how is cmake actually finding OpenNI? Using this file? Or some other way?

Thanks :)

Answer 1

Yes, CMake uses file you mentioned to find OpenNI. The OPENNI_FOUND variable is set by find_package_handle_standard_args() function. It is where the all magic is done, see the documentation for it .