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+# Adding Export Configuration #
+
+During Step 4 of the tutorial we added the ability for CMake to install the
+library and headers of the project. During Step 7 we added the ability
+to package up this information so it could be distributed to other people.
+
+The next step is to add the necessary information so that other CMake projects
+can use our project, be it from a build directory, a local install or when
+packaged.
+
+The first step is to update our install(TARGETS) commands to not only specify
+a DESTINATION but also an EXPORT. The EXPORT keyword generates and installs a
+CMake file containing code to import all targets listed in the install command
+from the installation tree. So let's go ahead and explicitly EXPORT the
+MathFunctions library by updating the install command in
+MathFunctions/CMakeLists.txt to look like:
+
+  install(TARGETS MathFunctions DESTINATION lib EXPORT MathFunctionsTargets)
+
+Now that we have MathFunctions being exported, we also need to explicitly install
+the generated MathFunctionsTargets.cmake file. This is done by adding
+the following to the bottom of the top-level CMakeLists.txt:
+
+  # install the configuration targets
+  install(EXPORT MathFunctionsTargets
+    FILE MathFunctionsTargets.cmake
+    DESTINATION lib/cmake/MathFunctions
+  )
+
+At this point you should try and run CMake. If everything is setup properly
+you will see that CMake will generate an error that looks like:
+
+  Target "MathFunctions" INTERFACE_INCLUDE_DIRECTORIES property contains
+  path:
+
+    "/Users/robert/Documents/CMakeClass/Tutorial/Step11/MathFunctions"
+
+  which is prefixed in the source directory.
+
+What CMake is trying to say is that during generating the export information
+it will export a path that is intrinsically tied to the current machine and
+will not be valid on other machines. The solution to this is to update the
+MathFunctions target_include_directories to understand that it needs different
+INTERFACE locations when being used from within the build directory and from an
+install / package. This means converting the target_include_directories
+call for MathFunctions to look like:
+
+  target_include_directories(MathFunctions
+                             INTERFACE
+                              $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+                              $<INSTALL_INTERFACE:include>
+                             )
+
+Once this has been updated, we can re-run CMake and see verify that it doesn't
+warn anymore.
+
+At this point, we have CMake properly packaging the target information that is
+required but we will still need to generate a MathFunctionsConfig.cmake, so
+that the CMake find_package command can find our project. So let's go ahead and
+add a new file to the top-level of the project called Config.cmake.in with the
+following contents:
+
+  @PACKAGE_INIT@
+
+  include ( "${CMAKE_CURRENT_LIST_DIR}/MathFunctionsTargets.cmake" )
+
+Then, to properly configure and install that file, add the following to the
+bottom of the top-level CMakeLists:
+
+  include(CMakePackageConfigHelpers)
+  # generate the config file that is includes the exports
+  configure_package_config_file(${CMAKE_CURRENT_SOURCE_DIR}/Config.cmake.in
+    "${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfig.cmake"
+    INSTALL_DESTINATION "lib/cmake/example"
+    NO_SET_AND_CHECK_MACRO
+    NO_CHECK_REQUIRED_COMPONENTS_MACRO
+    )
+  # generate the version file for the config file
+  write_basic_package_version_file(
+    "${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfigVersion.cmake"
+    VERSION "${Tutorial_VERSION_MAJOR}.${Tutorial_VERSION_MINOR}"
+    COMPATIBILITY AnyNewerVersion
+  )
+
+  # install the configuration file
+  install(FILES
+    ${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfig.cmake
+    DESTINATION lib/cmake/MathFunctions
+    )
+
+At this point, we have generated a relocatable CMake Configuration for our project
+that can be used after the project has been installed or packaged. If we want
+our project to also be used from a build directory we only have to add
+the following to the bottom of the top level CMakeLists:
+
+  # generate the export targets for the build tree
+  # needs to be after the install(TARGETS ) command
+  export(EXPORT MathFunctionsTargets
+    FILE "${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsTargets.cmake"
+  )
+
+With this export call we now generate a Targets.cmake, allowing the configured
+MathFunctionsConfig.cmake in the build directory to be used by other projects,
+without needing it to be installed.