Tutorial: Update step 2 style
This commit is contained in:
Markus Ferrell
parent
5b949bbb91
commit
80f5d28813
@ -160,7 +160,7 @@ The last command to call for a basic project is
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:name: CMakeLists.txt-add_executable
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:language: cmake
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:start-after: # add the executable
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:end-before: # add the binary tree to the search path for include files
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:end-before: # TODO 9:
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.. raw:: html
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@ -240,7 +240,7 @@ the following:
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:name: tutorial.cxx-cxx11
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:language: c++
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:start-after: // convert input to double
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:end-before: // calculate square root
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:end-before: // TODO 12:
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.. raw:: html
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@ -265,7 +265,7 @@ add the :variable:`CMAKE_CXX_STANDARD` declarations above the call to
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:name: CMakeLists.txt-CXX_STANDARD
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:language: cmake
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:start-after: # specify the C++ standard
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:end-before: # configure a header file to pass some of the CMake settings
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:end-before: # TODO 7:
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.. raw:: html
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@ -345,7 +345,7 @@ lets us maintain a single source of data for the version number.
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First, we modify the ``CMakeLists.txt`` file to use the
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:command:`project` command to set both the project name and version number.
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When the command:`project` command is called, CMake defines
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When the :command:`project` command is called, CMake defines
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``Tutorial_VERSION_MAJOR`` and ``Tutorial_VERSION_MINOR`` behind the scenes.
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.. raw:: html
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@ -375,7 +375,7 @@ specified CMake variables replaced:
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:name: CMakeLists.txt-configure_file
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:language: cmake
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:start-after: # to the source code
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:end-before: # add the executable
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:end-before: # TODO 8:
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.. raw:: html
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@ -420,6 +420,7 @@ be replaced with the corresponding version numbers from the project in
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:caption: TODO 10: TutorialConfig.h.in
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:name: TutorialConfig.h.in
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:language: c++
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:end-before: // TODO 13:
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.. raw:: html
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@ -1,136 +1,457 @@
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Step 2: Adding a Library
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========================
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Now we will add a library to our project. This library will contain our own
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At this point, we have seen how to create a basic project using CMake. In this
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step, we will learn how to create and use a library in our project. We will
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also see how to make the use of our library optional.
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Exercise 1 - Creating a Library
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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To add a library in CMake, use the :command:`add_library` command and specify
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which source files should make up the library.
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Rather than placing all of the source files in one directory, we can organize
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our project with one or more subdirectories. In this case, we will create a
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subdirectory specifically for our library. Here, we can add a new
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``CMakeLists.txt`` file and one or more source files. In the top level
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``CMakeLists.txt`` file, we will use the :command:`add_subdirectory` command
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to add the subdirectory to the build.
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Once the library is created, it is connected to our executable target with
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:command:`target_include_directories` and :command:`target_link_libraries`.
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Goal
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----
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Add and use a library.
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Helpful Resources
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-----------------
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* :command:`add_library`
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* :command:`add_subdirectory`
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* :command:`target_include_directories`
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* :command:`target_link_libraries`
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* :variable:`PROJECT_SOURCE_DIR`
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Files to Edit
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-------------
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* ``CMakeLists.txt``
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* ``tutorial.cxx``
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* ``MathFunctions/CMakeLists.txt``
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Getting Started
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---------------
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In this exercise, we will add a library to our project that contains our own
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implementation for computing the square root of a number. The executable can
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then use this library instead of the standard square root function provided by
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the compiler.
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For this tutorial we will put the library into a subdirectory
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called ``MathFunctions``. This directory already contains a header file,
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``MathFunctions.h``, and a source file ``mysqrt.cxx``. The source file has one
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function called ``mysqrt`` that provides similar functionality to the
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compiler's ``sqrt`` function.
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For this tutorial we will put the library into a subdirectory called
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``MathFunctions``. This directory already contains a header file,
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``MathFunctions.h``, and a source file ``mysqrt.cxx``. We will not need to
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modify either of these files. The source file has one function called
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``mysqrt`` that provides similar functionality to the compiler's ``sqrt``
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function.
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Add the following one line ``CMakeLists.txt`` file to the ``MathFunctions``
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directory:
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From the ``Help/guide/tutorial/Step2`` directory, start with ``TODO 1`` and
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complete through ``TODO 6``.
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.. literalinclude:: Step3/MathFunctions/CMakeLists.txt
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:caption: MathFunctions/CMakeLists.txt
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:name: MathFunctions/CMakeLists.txt
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:language: cmake
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First, fill in the one line ``CMakeLists.txt`` in the ``MathFunctions``
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subdirectory.
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To make use of the new library we will add an :command:`add_subdirectory`
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call in the top-level ``CMakeLists.txt`` file so that the library will get
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built. We add the new library to the executable, and add ``MathFunctions`` as
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an include directory so that the ``MathFunctions.h`` header file can be found.
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The last few lines of the top-level ``CMakeLists.txt`` file should now look
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like:
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Next, edit the top level ``CMakeLists.txt``.
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.. code-block:: cmake
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-add_subdirectory
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Finally, use the newly created ``MathFunctions`` library in ``tutorial.cxx``
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# add the MathFunctions library
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add_subdirectory(MathFunctions)
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# add the executable
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add_executable(Tutorial tutorial.cxx)
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target_link_libraries(Tutorial PUBLIC MathFunctions)
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# add the binary tree to the search path for include files
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# so that we will find TutorialConfig.h
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target_include_directories(Tutorial PUBLIC
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"${PROJECT_BINARY_DIR}"
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"${PROJECT_SOURCE_DIR}/MathFunctions"
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)
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Now let us make the ``MathFunctions`` library optional. While for the tutorial
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there really isn't any need to do so, for larger projects this is a common
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occurrence. The first step is to add an option to the top-level
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``CMakeLists.txt`` file.
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.. literalinclude:: Step3/CMakeLists.txt
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-option
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:language: cmake
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:start-after: # should we use our own math functions
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:end-before: # add the MathFunctions library
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This option will be displayed in the :manual:`cmake-gui <cmake-gui(1)>` and
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:manual:`ccmake <ccmake(1)>`
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with a default value of ``ON`` that can be changed by the user. This setting
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will be stored in the cache so that the user does not need to set the value
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each time they run CMake on a build directory.
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The next change is to make building and linking the ``MathFunctions`` library
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conditional. To do this, we will create an ``if`` statement which checks the
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value of the option. Inside the ``if`` block, put the
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:command:`add_subdirectory` command from above with some additional list
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commands to store information needed to link to the library and add the
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subdirectory as an include directory in the ``Tutorial`` target.
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The end of the top-level ``CMakeLists.txt`` file will now look like the
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following:
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.. literalinclude:: Step3/CMakeLists.txt
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-target_link_libraries-EXTRA_LIBS
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:language: cmake
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:start-after: # add the MathFunctions library
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Note the use of the variable ``EXTRA_LIBS`` to collect up any optional
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libraries to later be linked into the executable. The variable
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``EXTRA_INCLUDES`` is used similarly for optional header files. This is a
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classic approach when dealing with many optional components, we will cover
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the modern approach in the next step.
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The corresponding changes to the source code are fairly straightforward.
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First, in ``tutorial.cxx``, include the ``MathFunctions.h`` header if we
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need it:
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.. literalinclude:: Step3/tutorial.cxx
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:caption: tutorial.cxx
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:name: tutorial.cxx-ifdef-include
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:language: c++
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:start-after: // should we include the MathFunctions header
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:end-before: int main
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Then, in the same file, make ``USE_MYMATH`` control which square root
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function is used:
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.. literalinclude:: Step3/tutorial.cxx
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:caption: tutorial.cxx
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:name: tutorial.cxx-ifdef-const
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:language: c++
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:start-after: // which square root function should we use?
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:end-before: std::cout << "The square root of
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Since the source code now requires ``USE_MYMATH`` we can add it to
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``TutorialConfig.h.in`` with the following line:
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.. literalinclude:: Step3/TutorialConfig.h.in
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:caption: TutorialConfig.h.in
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:name: TutorialConfig.h.in-cmakedefine
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:language: c++
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:lines: 4
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**Exercise**: Why is it important that we configure ``TutorialConfig.h.in``
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after the option for ``USE_MYMATH``? What would happen if we inverted the two?
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Build and Run
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-------------
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Run the :manual:`cmake <cmake(1)>` executable or the
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:manual:`cmake-gui <cmake-gui(1)>` to configure the project and then build it
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with your chosen build tool. Then run the built Tutorial executable.
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with your chosen build tool.
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Now let's update the value of ``USE_MYMATH``. The easiest way is to use the
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:manual:`cmake-gui <cmake-gui(1)>` or :manual:`ccmake <ccmake(1)>` if you're
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in the terminal. Or, alternatively, if you want to change the option from the
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command-line, try:
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Below is a refresher of what that looks like from the command line:
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.. code-block:: console
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mkdir Step2_build
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cd Step2_build
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cmake ../Step2
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cmake --build .
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Try to use the newly built ``Tutorial`` and ensure that it is still
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producing accurate square root values.
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Solution
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--------
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In the ``CMakeLists.txt`` file in the ``MathFunctions`` directory, we create
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a library target called ``MathFunctions`` with :command:`add_library`. The
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source file for the library is passed as an argument to
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:command:`add_library`. This looks like the following line:
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.. raw:: html
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<details><summary>TODO 1: Click to show/hide answer</summary>
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.. literalinclude:: Step3/MathFunctions/CMakeLists.txt
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:caption: TODO 1: MathFunctions/CMakeLists.txt
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:name: MathFunctions/CMakeLists.txt-add_library
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:language: cmake
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.. raw:: html
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</details>
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To make use of the new library we will add an :command:`add_subdirectory`
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call in the top-level ``CMakeLists.txt`` file so that the library will get
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built.
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.. raw:: html
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<details><summary>TODO 2: Click to show/hide answer</summary>
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.. code-block:: cmake
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:caption: TODO 2: CMakeLists.txt
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:name: CMakeLists.txt-add_subdirectory
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add_subdirectory(MathFunctions)
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.. raw:: html
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</details>
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Next, the new library target is linked to the executable target using
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:command:`target_link_libraries`.
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.. raw:: html
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<details><summary>TODO 3: Click to show/hide answer</summary>
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.. code-block:: cmake
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:caption: TODO 3: CMakeLists.txt
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:name: CMakeLists.txt-target_link_libraries
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target_link_libraries(Tutorial PUBLIC MathFunctions)
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.. raw:: html
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</details>
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Finally we need to specify the library's header file location. Modify
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:command:`target_include_directories` to add the ``MathFunctions`` subdirectory
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as an include directory so that the ``MathFunctions.h`` header file can be
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found.
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.. raw:: html
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<details><summary>TODO 4: Click to show/hide answer</summary>
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.. code-block:: cmake
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:caption: TODO 4: CMakeLists.txt
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:name: CMakeLists.txt-target_include_directories-step2
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target_include_directories(Tutorial PUBLIC
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"${PROJECT_BINARY_DIR}"
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"${PROJECT_SOURCE_DIR}/MathFunctions"
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)
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.. raw:: html
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</details>
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Now let's use our library. In ``tutorial.cxx``, include ``MathFunctions.h``:
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.. raw:: html
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<details><summary>TODO 5: Click to show/hide answer</summary>
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.. code-block:: c++
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:caption: TODO 5 : tutorial.cxx
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:name: tutorial.cxx-include_MathFunctions.h
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#include "MathFunctions.h"
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.. raw:: html
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</details>
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Lastly, replace ``sqrt`` with our library function ``mysqrt``.
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.. raw:: html
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<details><summary>TODO 6: Click to show/hide answer</summary>
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.. code-block:: c++
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:caption: TODO 6 : tutorial.cxx
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:name: tutorial.cxx-call_mysqrt
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const double outputValue = mysqrt(inputValue);
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.. raw:: html
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</details>
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Exercise 2 - Making Our Library Optional
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Now let us make the MathFunctions library optional. While for the tutorial
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there really isn't any need to do so, for larger projects this is a common
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occurrence.
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CMake can do this using the :command:`option` command. This gives users a
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variable which they can change when configuring their cmake build. This
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setting will be stored in the cache so that the user does not need to set
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the value each time they run CMake on a build directory.
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Goal
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----
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Add the option to build without ``MathFunctions``.
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Helpful Resources
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-----------------
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* :command:`if`
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* :command:`list`
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* :command:`option`
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* :command:`cmakedefine <configure_file>`
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Files to Edit
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-------------
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* ``CMakeLists.txt``
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* ``tutorial.cxx``
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* ``TutorialConfig.h.in``
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Getting Started
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---------------
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Start with the resulting files from Exercise 1. Complete ``TODO 7`` through
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``TODO 13``.
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First create a variable ``MY_MATH`` using the :command:`option` command
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in the top-level ``CMakeLists.txt`` file. In that same file, use that option
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to determine whether to build and use the ``MathFunctions`` library.
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Then, update ``tutorial.cxx`` and ``TutorialConfig.h.in`` to use ``MY_MATH``.
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Build and Run
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-------------
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Since we have our build directory already configured from Exercise 1, we can
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rebuild by simply calling the following:
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.. code-block:: console
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cd ../Step2_build
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cmake --build .
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Next, run the ``Tutorial`` executable on a few numbers to verify that it's
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still correct.
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Now let's update the value of ``USE_MYMATH`` to ``OFF``. The easiest way is to
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use the :manual:`cmake-gui <cmake-gui(1)>` or :manual:`ccmake <ccmake(1)>`
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if you're in the terminal. Or, alternatively, if you want to change the
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option from the command-line, try:
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.. code-block:: console
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cmake ../Step2 -DUSE_MYMATH=OFF
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Rebuild and run the tutorial again.
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Now, rebuild the code with the following:
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Which function gives better results, ``sqrt`` or ``mysqrt``?
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.. code-block:: console
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cmake --build .
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Then, run the executable again to ensure that it still works with
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``USE_MYMATH`` set to ``OFF``. Which function gives better results, ``sqrt``
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or ``mysqrt``?
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Solution
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--------
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The first step is to add an option to the top-level ``CMakeLists.txt`` file.
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This option will be displayed in the :manual:`cmake-gui <cmake-gui(1)>` and
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:manual:`ccmake <ccmake(1)>` with a default value of ``ON`` that can be
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changed by the user.
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.. raw:: html
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<details><summary>TODO 7: Click to show/hide answer</summary>
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.. literalinclude:: Step3/CMakeLists.txt
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:caption: TODO 7: CMakeLists.txt
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:name: CMakeLists.txt-option
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:language: cmake
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:start-after: # should we use our own math functions
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:end-before: # configure a header file to pass some of the CMake settings
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.. raw:: html
|
||||
|
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</details>
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|
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Next, make building and linking the ``MathFunctions`` library
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conditional.
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Start by creating a :command:`list` of the optional library targets for our
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project. At the moment, it is just ``MathFunctions``. Let's name our list
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``EXTRA_LIBS``.
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Similarly, we need to make a :command:`list` for the optional includes which
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we will call ``EXTRA_INCLUDES``. In this list, we will ``APPEND`` the path of
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the header file needed for our library.
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Next, create an :command:`if` statement which checks the value of
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``USE_MYMATH``. Inside the :command:`if` block, put the
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:command:`add_subdirectory` command from Exercise 1 with the additional
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:command:`list` commands.
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When ``MY_MATH`` is ``ON``, the lists will be generated and will be added to
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our project. When ``MY_MATH`` is ``OFF``, the lists stay empty. With this
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strategy, we allow users to toggle ``MY_MATH`` to manipulate what library is
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used in the build.
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The top-level CMakeLists.txt file will now look like the following:
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||||
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.. raw:: html
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||||
|
||||
<details><summary>TODO 8: Click to show/hide answer</summary>
|
||||
|
||||
.. literalinclude:: Step3/CMakeLists.txt
|
||||
:caption: TODO 8: CMakeLists.txt
|
||||
:name: CMakeLists.txt-USE_MYMATH
|
||||
:language: cmake
|
||||
:start-after: # add the MathFunctions library
|
||||
:end-before: # add the executable
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
Now that we have these two lists, we need to update
|
||||
:command:`target_link_libraries` and :command:`target_include_directories` to
|
||||
use them. Changing them is fairly straightforward.
|
||||
|
||||
For :command:`target_link_libraries`, we replace the written out
|
||||
library names with ``EXTRA_LIBS``. This looks like the following:
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<details><summary>TODO 9: Click to show/hide answer</summary>
|
||||
|
||||
.. literalinclude:: Step3/CMakeLists.txt
|
||||
:caption: TODO 9: CMakeLists.txt
|
||||
:name: CMakeLists.txt-target_link_libraries-EXTRA_LIBS
|
||||
:language: cmake
|
||||
:start-after: add_executable(Tutorial tutorial.cxx)
|
||||
:end-before: # add the binary tree to the search path for include files
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
Then, we do the same thing with :command:`target_include_directories` and
|
||||
``EXTRA_INCLUDES``.
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<details><summary>TODO 10: Click to show/hide answer</summary>
|
||||
|
||||
.. literalinclude:: Step3/CMakeLists.txt
|
||||
:caption: TODO 10 : CMakeLists.txt
|
||||
:name: CMakeLists.txt-target_link_libraries-EXTRA_INCLUDES
|
||||
:language: cmake
|
||||
:start-after: # so that we will find TutorialConfig.h
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
Note that this is a classic approach when dealing with many components. We
|
||||
will cover the modern approach in the Step 3 of the tutorial.
|
||||
|
||||
The corresponding changes to the source code are fairly straightforward.
|
||||
First, in ``tutorial.cxx``, we include the ``MathFunctions.h`` header if
|
||||
``MY_MATH`` is defined.
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<details><summary>TODO 11: Click to show/hide answer</summary>
|
||||
|
||||
.. literalinclude:: Step3/tutorial.cxx
|
||||
:caption: TODO 11 : tutorial.cxx
|
||||
:name: tutorial.cxx-ifdef-include
|
||||
:language: c++
|
||||
:start-after: // should we include the MathFunctions header
|
||||
:end-before: int main
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
Then, in the same file, we make ``USE_MYMATH`` control which square root
|
||||
function is used:
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<details><summary>TODO 12: Click to show/hide answer</summary>
|
||||
|
||||
.. literalinclude:: Step3/tutorial.cxx
|
||||
:caption: TODO 12 : tutorial.cxx
|
||||
:name: tutorial.cxx-ifdef-const
|
||||
:language: c++
|
||||
:start-after: // which square root function should we use?
|
||||
:end-before: std::cout << "The square root of
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
Since the source code now requires ``USE_MYMATH`` we can add it to
|
||||
``TutorialConfig.h.in`` with the following line:
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<details><summary>TODO 13: Click to show/hide answer</summary>
|
||||
|
||||
.. literalinclude:: Step3/TutorialConfig.h.in
|
||||
:caption: TODO 13 : TutorialConfig.h.in
|
||||
:name: TutorialConfig.h.in-cmakedefine
|
||||
:language: c++
|
||||
:lines: 4
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
With these changes, our library is now completely optional to whoever is
|
||||
building and using it.
|
||||
|
||||
Bonus Question
|
||||
--------------
|
||||
|
||||
Why is it important that we configure ``TutorialConfig.h.in``
|
||||
after the option for ``USE_MYMATH``? What would happen if we inverted the two?
|
||||
|
||||
Answer
|
||||
------
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<details><summary>Click to show/hide answer</summary>
|
||||
|
||||
We configure after because ``TutorialConfig.h.in`` uses the value of
|
||||
``USE_MYMATH``. If we configure the file before
|
||||
calling :command:`option`, we won't be using the expected value of
|
||||
``USE_MYMATH``.
|
||||
|
||||
.. raw:: html
|
||||
|
||||
</details>
|
||||
|
||||
@ -7,13 +7,36 @@ project(Tutorial VERSION 1.0)
|
||||
set(CMAKE_CXX_STANDARD 11)
|
||||
set(CMAKE_CXX_STANDARD_REQUIRED True)
|
||||
|
||||
# TODO 7: Create a variable MY_MATH using option and set default to ON
|
||||
|
||||
# configure a header file to pass some of the CMake settings
|
||||
# to the source code
|
||||
configure_file(TutorialConfig.h.in TutorialConfig.h)
|
||||
|
||||
# TODO 8: Use list() and APPEND to create a list of optional libraries
|
||||
# called EXTRA_LIBS and a list of optional include directories called
|
||||
# EXTRA_INCLUDES. Add the MathFunctions library and source directory to
|
||||
# the appropriate lists.
|
||||
#
|
||||
# Only call add_subdirectory and only add MathFunctions specific values
|
||||
# to EXTRA_LIBS and EXTRA_INCLUDES if USE_MYMATH is true.
|
||||
|
||||
# TODO 2: Use add_subdirectory() to add MathFunctions to this project
|
||||
|
||||
# add the executable
|
||||
add_executable(Tutorial tutorial.cxx)
|
||||
|
||||
# TODO 9: Use EXTRA_LIBS instead of the MathFunctions specific values
|
||||
# in target_link_libraries.
|
||||
|
||||
# TODO 3: Use target_link_libraries to link the library to our executable
|
||||
|
||||
# TODO 4: Add MathFunctions to Tutorial's target_include_directories()
|
||||
# Hint: ${PROJECT_SOURCE_DIR} is a path to the project source. AKA This folder!
|
||||
|
||||
# TODO 10: Use EXTRA_INCLUDES instead of the MathFunctions specific values
|
||||
# in target_include_directories.
|
||||
|
||||
# add the binary tree to the search path for include files
|
||||
# so that we will find TutorialConfig.h
|
||||
target_include_directories(Tutorial PUBLIC
|
||||
|
||||
2
Help/guide/tutorial/Step2/MathFunctions/CMakeLists.txt
Normal file
2
Help/guide/tutorial/Step2/MathFunctions/CMakeLists.txt
Normal file
@ -0,0 +1,2 @@
|
||||
# TODO 1: Add a library called MathFunctions
|
||||
# Hint: You will need the add_library command
|
||||
@ -1,3 +1,5 @@
|
||||
// the configured options and settings for Tutorial
|
||||
#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
|
||||
#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@
|
||||
|
||||
// TODO 13: use cmakedefine to define MY_MATH
|
||||
|
||||
@ -5,6 +5,10 @@
|
||||
|
||||
#include "TutorialConfig.h"
|
||||
|
||||
// TODO 11: Only include MathFunctions if MY_MATH is defined
|
||||
|
||||
// TODO 5: Include MathFunctions.h
|
||||
|
||||
int main(int argc, char* argv[])
|
||||
{
|
||||
if (argc < 2) {
|
||||
@ -18,6 +22,10 @@ int main(int argc, char* argv[])
|
||||
// convert input to double
|
||||
const double inputValue = std::stod(argv[1]);
|
||||
|
||||
// TODO 12: Use mysqrt if MY_MATH is defined and sqrt otherwise
|
||||
|
||||
// TODO 6: Replace sqrt with mysqrt
|
||||
|
||||
// calculate square root
|
||||
const double outputValue = sqrt(inputValue);
|
||||
std::cout << "The square root of " << inputValue << " is " << outputValue
|
||||
|
||||
Loading…
Reference in New Issue
Block a user