CODEWITHSUNDEEP
c++cmakedependencieslibraries
CD86
CD86

Reputation: 1089

Adding third-party libs to my CMake Project

I cant seem to wrap my head around a certain train of thoughts and was hoping you guys could help me seeing things more clearly. As I understand the find_package command should be all whats necessary to import third-party dependencies into my projects in modern cmake.

  1. Is it considered good practice to use those commands always in the root CMakeLists.txt of my Project hierarchy that features several subfolders, that are added with add_subdirectory.()? Or should I use find_package in the subdirectory where it is actually needed?

  2. I dont get the difference between Find.cmake and Config.cmake files. I believe Config.cmake files are the result of a library author correctly exporting the targets of his lib while Find.cmake files are like an auxiliary measure if a lib does not provide cmake-support, i.e. do not support clients to use CMake. But CMake itself might offer suitable Find.cmake files for proper adoption. Correct? So when do I have to install and export my lib?

thank your for your help

EDIT:

thank you for your hep Thomas. As a concrete example, I would like to add libQGLViewer as a third-party library to my project. However, the package-manager under Ubuntu 16.04 only offers an older version which depends on Qt4. Still, my project uses Qt5 and so I thought, I just download the lib and build it from source to /opt, no sweat. libQGLViewer uses qmake and so I turned to google and found a FindQGLViewer.cmake file. I copied this file to /usr/share/cmake-3.5/Modules and as I understand, this should render the command find_package(QGLViewer) to complete succesfully upon which the Variables ${QGLViewer_LIBRARIES} etc. are populated. However, it doesnt work and I cant figure out what the problem is, probably due to a general lack of understanding regarding these matters

    CMake Warning at /usr/share/cmake 3.5/Modules/FindQGLViewer.cmake:108 (MESSAGE):
  Could not find libQGLViewer.so, failed to build?
  Call Stack (most recent call first):
  CMakeLists.txt:57 (_find_package)
  CMakeLists.txt:109 (find_package)

Upvotes: 2

Views: 2605

Answers (1)

thomas_f
thomas_f

Reputation: 1993

1. This depends on your project structure. If you invoke find_package() before adding any sub-folders, then you will ensure that the package is available to all sub-folders. If you instead invoke find_package() in one of the sub-folders, then that package will only be available after the fact.

If there is a chance that more than one sub-folder will depend on the package and at least one of these sub-folders is always part of the build (i.e. not optional), then the prudent thing to do would be to invoke find_package() at top-level before adding the sub-folders to ensure its availability to all sub-folders that might need it, without having to consider the order in which you add the sub-folders.

2. Your understanding is largely correct. Here is the official explanation. Yes, CMake ships with a number of Find-modules for common libraries, but the list is far from exhaustive even in terms of common libraries.

Upvotes: 0

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