How to Create Packages with CMake

.
+-- MyPack
|   +-- Lib1
|   |   +-- include
|   |   |   +-- Lib1.h
|   |   +-- src
|   |   |   +-- Lib2.cpp
|   |   +-- CMakeLists.txt
|   +-- Lib2
|   |   +-- include
|   |   |   +-- Lib2.h
|   |   +-- src
|   |   |   +-- Lib2.cpp
|   |   +-- CMakeLists.txt
|   +-- CMakeLists.txt
+-- SubProject1
|   +-- CMakeLists.txt
+-- SubProject2
|   +-- CMakeLists.txt
+-- CMakeLists.txt

Hi all.

I'm new to CMake and I'm trying to obtain something like the following. Considering the above directory tree of my C++ project:

I have a directory (let's say "MyPack") that contains several subdirectories (Lib1, Lib2...) and each one represents a C++ Library that I wrote.

How can I setup everything so I can write find_package(MyPack)in the other subprojects?

Every subproject is a stand-alone project, and does not depend on other subprojects, but just on libraries in "MyPack".

Solution

Your drawing is a bit confusing because there is a CMakeLists.txt after Lib2 which belongs to no folder... Anyway: is MyPack

Lib1 and Lib2?
Lib1/Lib2/Subproj1/Subproj2?

in the 2nd case:

The top directory CMakeLists.txt gives you access to targets of Lib1 and Lib2 that you can use in SubProject1 and SubProject2 if you have something like this:

project(MyPack)
add_subdirectory(Lib1) # Building Lib1
add_subdirectory(Lib2) # Building Lib2
add_subdirectory(SubProject1) # you can use Lib1 & Lib2 targets here
add_subdirectory(SubProject2) # you can use Lib1 & Lib2 targets here

If it is the 1st case, MyPack is only Lib1 and Lib2 :

Using find_package(MyPack) means that you need to create a Config file and install() your project:

project(MyPack)
add_subdirectory(Lib1)
add_subdirectory(Lib2)

in Lib1/CMakeLists.txt:

add_library(lib1 "")
add_library(MyPack::lib1 ALIAS lib1)
[...]
include(GNUInstallDirs)
install( 
  TARGETS lib1
  EXPORT MyPackTargets
  ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
  )

in Lib2/CMakeLists.txt:

add_library(lib2 "")
add_library(MyPack::lib2 ALIAS lib2)
[...]
include(GNUInstallDirs)
install( 
  TARGETS lib2
  EXPORT MyPackTargets
  ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
  )

Now you have lib1 and lib2 in the export MyPackTargets. You have to install that export as well.

anywhere after above:

install(
  EXPORT MyPackTargets
  DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/MyPack
  NAMESPACE MyPack::
  FILE MyPackTargets.cmake # Not sure if this is still needed
  )

include(CMakePackageConfigHelpers)
configure_package_config_file( 
  "Config.cmake.in" 
  "MyPackConfig.cmake"
  INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/MyPack
  PATH_VARS
    CMAKE_INSTALL_LIBDIR
  )

write_basic_package_version_file(
  ${CMAKE_CURRENT_BINARY_DIR}/MyPackConfigVersion.cmake
  VERSION 1.0.0
  COMPATIBILITY SameMajorVersion
  )

### Install Config and ConfigVersion files
install(
  FILES "${CMAKE_CURRENT_BINARY_DIR}/MyPackConfig.cmake"
        "${CMAKE_CURRENT_BINARY_DIR}/MyPackConfigVersion.cmake"
  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/MyPack"
  )

create a file Config.cmake.in with:

@PACKAGE_INIT@
include( "${CMAKE_CURRENT_LIST_DIR}/MyPackTargets.cmake" )

Now if you build and install your project MyPack, find_package(MyPack) from other project should find it and import the targets you've created.

Here is some documentation: https://cmake.org/cmake/help/latest/module/CMakePackageConfigHelpers.html

https://blog.kitware.com/cmake-superbuilds-git-submodules/