Help/guide/tutorial/Before You Begin.rst - third_party/cmake - Git at Google

 Step 0: Before You Begin
 ========================

 The CMake tutorial consists of hands-on exercises writing and building a
 C++ project; solving progressively more complex build requirements such
 as libraries, code generators, tests, and external dependencies. Before we
 are ready to even begin the first step of that journey, we need to ensure we
 have the correct tools at hand and understand how to use them.

 .. note::
   The tutorial material assumes the user has a C++20 compiler and toolchain
   available, and at least a beginner understanding of the C++ language. It
   is impossible to cover here all the possible ways one might acquire these
   prerequisites.

 This prerequisite step provides recommendations for how to acquire and
 run CMake itself in order to carry out the rest of the tutorial. If you're
 already familiar with the basics of how to run CMake, you can feel free to move
 on to the rest of the tutorial.

 Getting the Tutorial Exercises
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 .. include:: include/source.rst

 |tutorial_source|
 Each step of the tutorial has a corresponding subfolder, which serves as the
 starting point for that step's exercises.

 Getting CMake
 ^^^^^^^^^^^^^

 The most obvious way to get your hands on CMake is to download it from the
 CMake website. `The website's "Download" section <https://cmake.org/download/>`_
 contains the latest builds of CMake for all common (and some uncommon) desktop
 platforms.

 However, it is preferable to acquire CMake via the usual delivery mechanism for
 developer tools on your platform. CMake is available in most packaging
 repositories, as a Visual Studio component, and can even be installed from the
 Python package index. Additionally, CMake is often available as part of the base
 image of most CI/CD runners targeting C/C++. You should consult the documentation
 for your software build environment to see if CMake is already available.

 CMake can also be compiled from source using the instructions described by
 ``README.rst``, found in the root of the CMake source tree.

 CMake, like any program, needs to be available in ``PATH`` in order to be run
 from a shell. You can verify CMake is available by running any CMake command.

 .. code-block:: shell

   $ cmake --version
   cmake version 3.23.5

   CMake suite maintained and supported by Kitware (kitware.com/cmake).


 .. note::
   If using a Visual Studio-provided development environment, it is best to run
   CMake from inside a Developer Command Prompt or Developer Powershell. This
   ensures CMake has access to all the required developer tooling and
   environment variables.

 CMake Generators
 ^^^^^^^^^^^^^^^^

 CMake is a configuration program, sometimes called a "meta" build system. As
 with other configuration systems, CMake is not ultimately responsible for
 running the commands which produce the software build. Instead, CMake generates
 a build system based on project, environment, and user-provided configuration
 information.

 CMake supports multiple build systems as the output of this configuration
 process. These output backends are called "generators", because they generate
 the build system. CMake supports many generators, the documentation for
 which can be found at :manual:`cmake-generators(7)`. Information about
 supported generators for your particular CMake installation can be found
 via :option:`cmake --help` under the "Generators" heading.

 Using CMake thus requires one of the build programs which consumes this
 generator output be available. The ``Unix Makefiles``, ``Ninja``, and
 ``Visual Studio`` generators require a compatible ``make``, ``ninja``, and
 ``Visual Studio`` installation respectively.

 .. note::
   The default generator on Windows is typically the newest available Visual
   Studio version on the machine running CMake, everywhere else it is
   ``Unix Makefiles``.

 Which generator is used can be controlled via the :envvar:`CMAKE_GENERATOR`
 environment variable, or the :option:`cmake -G` option.

 Single and Multi-Configuration Generators
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 In many cases, it is possible to treat the underlying build system as an
 implementation detail and not differentiate between, for example, ``ninja``
 and ``make`` when using CMake. However, there is one significant property
 of a given generator which we need to be aware of for even trivial workflows:
 if the generator supports single configuration builds, or if it supports
 multi-configuration builds.

 Software builds often have several variants which we might be interested in.
 These variants have names like ``Debug``, ``Release``, ``RelWithDebInfo``, and
 ``MinSizeRel``, with properties corresponding to the name of the given variant.

 A single-configuration build system always builds the software the same way, if
 it is generated to produce ``Debug`` builds it will always produce
 a ``Debug`` build. A multi-configuration build system can produce different
 outputs depending on the configuration specified at build time.

 .. note::
   The terms **build configuration** and **build type** are synonymous. When
   dealing with single-configuration generators, which only support a single
   variant, the generated variant is usually called the "build type".

   When dealing with multi-configuration generators, the available variants are
   usually called the "build configurations". Selecting a variant at build
   time is usually called "selecting a configuration" and referred to by flags
   and variables as the "config".

   However, this convention is not universal. Both technical and colloquial
   documentation often mix the two terms. *Configuration* and *config* are
   considered the more correct in contexts which generically address both single
   and multi-configuration generators.

 The commonly used generators are as follows:

 +-----------------------------+---------------------------------+
 | Single-Configuration        | Multi-Configuration             |
 +=============================+=================================+
 | :generator:`Ninja`          | :generator:`Ninja Multi-Config` |
 +-----------------------------+---------------------------------+
 | :generator:`Unix Makefiles` | Visual Studio (all versions)    |
 +-----------------------------+---------------------------------+
 | :generator:`FASTBuild`      | :generator:`Xcode`              |
 +-----------------------------+---------------------------------+

 When using a single-configuration generator, the build type is selected based on
 the :envvar:`CMAKE_BUILD_TYPE` environment variable, or can be specified
 directly when invoking CMake via ``cmake -DCMAKE_BUILD_TYPE=<config>``.

 .. note::
   For the purpose of the tutorial, it is generally unnecessary to specify a
   build type when working with single-configuration generators. The
   platform-specific default behavior will work for all exercises.

 When using a multi-configuration generator, the build configuration is specified
 at build time using either a build-system specific mechanism, or via the
 :option:`cmake --build --config <cmake--build --config>` option.

 Other Usage Basics
 ^^^^^^^^^^^^^^^^^^

 The rest of the tutorial will cover the remaining usage basics in greater depth,
 but for the purpose of ensuring we have a working development environment a few
 more CMake option flags will be enumerated here.


   :option:`cmake -S \<dir\> <cmake -S>`
     Specifies the project root directory, where CMake will find the project
     to be built. This contains the root ``CMakeLists.txt`` file which will
     be discussed in Step 1 of the tutorial.

     When unspecified, defaults to the current working directory.

   :option:`cmake -B \<dir\> <cmake -B>`
     Specifies the build directory, where CMake will output the files for the
     generated build system, as well as artifacts of the build itself when
     the build system is run.

     When unspecified, defaults to the current working directory.

   :option:`cmake --build \<dir\> <cmake --build>`
     Runs the build system in the specified build directory. This is a generic
     command for all generators. For multi-configuration generators, the desired
     configuration can be requested via:

     ``cmake --build <dir> --config <cfg>``

 Try It Out
 ^^^^^^^^^^

 The ``Help/guide/tutorial/Step0`` directory contains a simple "Hello World"
 C++ project. The specifics of how CMake configures this project will be
 discussed in Step 1 of the tutorial, we need only concern ourselves with
 running the CMake program itself.

 As described above, there are many possible ways we could run CMake depending
 on which generator we want to use for the build. If we navigate to the
 ``Help/guide/tutorial/Step0`` directory and run:

 .. code-block:: shell

   cmake -B build

 CMake will generate a build system for the Step0 project into
 ``Help/guide/tutorial/Step0/build`` using the default generator for the
 platform. Alternatively we can specify a specific generator, ``Ninja`` for
 example, with:

 .. code-block:: shell

   cmake -G Ninja -B build

 The effect is similar, but will use the ``Ninja`` generator instead of the
 platform default.

 .. note::
   We can't reuse the build directory with different generators. It is necessary
   to delete the build directory between CMake runs if you want to switch to a
   different generator using the same build directory.

 How we build and run the project after generating the build system depends on
 the kind of generator we're using. If it is a single-configuration generator on
 a non-Windows platform, we can simply do:

 .. code-block:: shell

   cmake --build build
   ./build/hello

 .. note::
   On Windows we might need to specify the file extension depending on which
   shell is in use, ie ``./build/hello.exe``

 If we're using a multi-configuration generator, we will want to specify the
 build configuration. The default configurations are ``Debug``, ``Release``,
 ``RelWithDebInfo``, and ``MinRelSize``. The result of the build will be stored
 in a configuration-specific subdirectory of the build folder. So for example we
 could run:

 .. code-block:: shell

   cmake --build build --config Debug
   ./build/Debug/hello

 Getting Help and Additional Resources
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 For help from the CMake community, you can reach out on
 `the CMake Discourse Forums <https://discourse.cmake.org/>`_.

 .. only:: cmakeorg

   For professional training related to CMake, please see
   `the CMake training landing page <https://www.kitware.com/courses/cmake-training/>`_.
   For other professional CMake services,
   `please reach out to us using our contact form <https://www.kitware.com/contact/>`_.
	Step 0: Before You Begin
	========================

	The CMake tutorial consists of hands-on exercises writing and building a
	C++ project; solving progressively more complex build requirements such
	as libraries, code generators, tests, and external dependencies. Before we
	are ready to even begin the first step of that journey, we need to ensure we
	have the correct tools at hand and understand how to use them.

	.. note::
	The tutorial material assumes the user has a C++20 compiler and toolchain
	available, and at least a beginner understanding of the C++ language. It
	is impossible to cover here all the possible ways one might acquire these
	prerequisites.

	This prerequisite step provides recommendations for how to acquire and
	run CMake itself in order to carry out the rest of the tutorial. If you're
	already familiar with the basics of how to run CMake, you can feel free to move
	on to the rest of the tutorial.

	Getting the Tutorial Exercises
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	.. include:: include/source.rst

	\|tutorial_source\|
	Each step of the tutorial has a corresponding subfolder, which serves as the
	starting point for that step's exercises.

	Getting CMake
	^^^^^^^^^^^^^

	The most obvious way to get your hands on CMake is to download it from the
	CMake website. `The website's "Download" section <https://cmake.org/download/>`_
	contains the latest builds of CMake for all common (and some uncommon) desktop
	platforms.

	However, it is preferable to acquire CMake via the usual delivery mechanism for
	developer tools on your platform. CMake is available in most packaging
	repositories, as a Visual Studio component, and can even be installed from the
	Python package index. Additionally, CMake is often available as part of the base
	image of most CI/CD runners targeting C/C++. You should consult the documentation
	for your software build environment to see if CMake is already available.

	CMake can also be compiled from source using the instructions described by
	``README.rst``, found in the root of the CMake source tree.

	CMake, like any program, needs to be available in ``PATH`` in order to be run
	from a shell. You can verify CMake is available by running any CMake command.

	.. code-block:: shell

	$ cmake --version
	cmake version 3.23.5

	CMake suite maintained and supported by Kitware (kitware.com/cmake).


	.. note::
	If using a Visual Studio-provided development environment, it is best to run
	CMake from inside a Developer Command Prompt or Developer Powershell. This
	ensures CMake has access to all the required developer tooling and
	environment variables.

	CMake Generators
	^^^^^^^^^^^^^^^^

	CMake is a configuration program, sometimes called a "meta" build system. As
	with other configuration systems, CMake is not ultimately responsible for
	running the commands which produce the software build. Instead, CMake generates
	a build system based on project, environment, and user-provided configuration
	information.

	CMake supports multiple build systems as the output of this configuration
	process. These output backends are called "generators", because they generate
	the build system. CMake supports many generators, the documentation for
	which can be found at :manual:`cmake-generators(7)`. Information about
	supported generators for your particular CMake installation can be found
	via :option:`cmake --help` under the "Generators" heading.

	Using CMake thus requires one of the build programs which consumes this
	generator output be available. The ``Unix Makefiles``, ``Ninja``, and
	``Visual Studio`` generators require a compatible ``make``, ``ninja``, and
	``Visual Studio`` installation respectively.

	.. note::
	The default generator on Windows is typically the newest available Visual
	Studio version on the machine running CMake, everywhere else it is
	``Unix Makefiles``.

	Which generator is used can be controlled via the :envvar:`CMAKE_GENERATOR`
	environment variable, or the :option:`cmake -G` option.

	Single and Multi-Configuration Generators
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	In many cases, it is possible to treat the underlying build system as an
	implementation detail and not differentiate between, for example, ``ninja``
	and ``make`` when using CMake. However, there is one significant property
	of a given generator which we need to be aware of for even trivial workflows:
	if the generator supports single configuration builds, or if it supports
	multi-configuration builds.

	Software builds often have several variants which we might be interested in.
	These variants have names like ``Debug``, ``Release``, ``RelWithDebInfo``, and
	``MinSizeRel``, with properties corresponding to the name of the given variant.

	A single-configuration build system always builds the software the same way, if
	it is generated to produce ``Debug`` builds it will always produce
	a ``Debug`` build. A multi-configuration build system can produce different
	outputs depending on the configuration specified at build time.

	.. note::
	The terms build configuration and build type are synonymous. When
	dealing with single-configuration generators, which only support a single
	variant, the generated variant is usually called the "build type".

	When dealing with multi-configuration generators, the available variants are
	usually called the "build configurations". Selecting a variant at build
	time is usually called "selecting a configuration" and referred to by flags
	and variables as the "config".

	However, this convention is not universal. Both technical and colloquial
	documentation often mix the two terms. Configuration and config are
	considered the more correct in contexts which generically address both single
	and multi-configuration generators.

	The commonly used generators are as follows:

	+-----------------------------+---------------------------------+
	\| Single-Configuration \| Multi-Configuration \|
	+=============================+=================================+
	\| :generator:`Ninja` \| :generator:`Ninja Multi-Config` \|
	+-----------------------------+---------------------------------+
	\| :generator:`Unix Makefiles` \| Visual Studio (all versions) \|
	+-----------------------------+---------------------------------+
	\| :generator:`FASTBuild` \| :generator:`Xcode` \|
	+-----------------------------+---------------------------------+

	When using a single-configuration generator, the build type is selected based on
	the :envvar:`CMAKE_BUILD_TYPE` environment variable, or can be specified
	directly when invoking CMake via ``cmake -DCMAKE_BUILD_TYPE=<config>``.

	.. note::
	For the purpose of the tutorial, it is generally unnecessary to specify a
	build type when working with single-configuration generators. The
	platform-specific default behavior will work for all exercises.

	When using a multi-configuration generator, the build configuration is specified
	at build time using either a build-system specific mechanism, or via the
	:option:`cmake --build --config <cmake--build --config>` option.

	Other Usage Basics
	^^^^^^^^^^^^^^^^^^

	The rest of the tutorial will cover the remaining usage basics in greater depth,
	but for the purpose of ensuring we have a working development environment a few
	more CMake option flags will be enumerated here.


	:option:`cmake -S \<dir\> <cmake -S>`
	Specifies the project root directory, where CMake will find the project
	to be built. This contains the root ``CMakeLists.txt`` file which will
	be discussed in Step 1 of the tutorial.

	When unspecified, defaults to the current working directory.

	:option:`cmake -B \<dir\> <cmake -B>`
	Specifies the build directory, where CMake will output the files for the
	generated build system, as well as artifacts of the build itself when
	the build system is run.

	When unspecified, defaults to the current working directory.

	:option:`cmake --build \<dir\> <cmake --build>`
	Runs the build system in the specified build directory. This is a generic
	command for all generators. For multi-configuration generators, the desired
	configuration can be requested via:

	``cmake --build <dir> --config <cfg>``

	Try It Out
	^^^^^^^^^^

	The ``Help/guide/tutorial/Step0`` directory contains a simple "Hello World"
	C++ project. The specifics of how CMake configures this project will be
	discussed in Step 1 of the tutorial, we need only concern ourselves with
	running the CMake program itself.

	As described above, there are many possible ways we could run CMake depending
	on which generator we want to use for the build. If we navigate to the
	``Help/guide/tutorial/Step0`` directory and run:

	.. code-block:: shell

	cmake -B build

	CMake will generate a build system for the Step0 project into
	``Help/guide/tutorial/Step0/build`` using the default generator for the
	platform. Alternatively we can specify a specific generator, ``Ninja`` for
	example, with:

	.. code-block:: shell

	cmake -G Ninja -B build

	The effect is similar, but will use the ``Ninja`` generator instead of the
	platform default.

	.. note::
	We can't reuse the build directory with different generators. It is necessary
	to delete the build directory between CMake runs if you want to switch to a
	different generator using the same build directory.

	How we build and run the project after generating the build system depends on
	the kind of generator we're using. If it is a single-configuration generator on
	a non-Windows platform, we can simply do:

	.. code-block:: shell

	cmake --build build
	./build/hello

	.. note::
	On Windows we might need to specify the file extension depending on which
	shell is in use, ie ``./build/hello.exe``

	If we're using a multi-configuration generator, we will want to specify the
	build configuration. The default configurations are ``Debug``, ``Release``,
	``RelWithDebInfo``, and ``MinRelSize``. The result of the build will be stored
	in a configuration-specific subdirectory of the build folder. So for example we
	could run:

	.. code-block:: shell

	cmake --build build --config Debug
	./build/Debug/hello

	Getting Help and Additional Resources
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	For help from the CMake community, you can reach out on
	`the CMake Discourse Forums <https://discourse.cmake.org/>`_.

	.. only:: cmakeorg

	For professional training related to CMake, please see
	`the CMake training landing page <https://www.kitware.com/courses/cmake-training/>`_.
	For other professional CMake services,
	`please reach out to us using our contact form <https://www.kitware.com/contact/>`_.