feaab27c1b
This commit moves the files under `subsys/cpp` directory to the `lib/cpp` directory because the C++ ABI runtime library and the standard C++ library components are not a "subsystem" (aka. API) in conventional sense and is better described as a "library." Classifying the C++ ABI runtime library and the standard C++ library as "libraries" instead of "subsystems" also better aligns with how the existing C standard library implementation (`lib/libc`) is handled. Signed-off-by: Stephanos Ioannidis <stephanos.ioannidis@nordicsemi.no>
107 lines
4.3 KiB
ReStructuredText
107 lines
4.3 KiB
ReStructuredText
.. _language_cpp:
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C++ Language Support
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####################
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C++ is a general-purpose object-oriented programming language that is based on
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the C language.
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Enabling C++ Support
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********************
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Zephyr supports applications written in both C and C++. However, to use C++ in
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an application you must configure Zephyr to include C++ support by selecting
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the :kconfig:option:`CONFIG_CPLUSPLUS` in the application configuration file.
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To enable C++ support, the compiler toolchain must also include a C++ compiler
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and the included compiler must be supported by the Zephyr build system. The
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:ref:`toolchain_zephyr_sdk`, which includes the GNU C++ Compiler (part of GCC),
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is supported by Zephyr, and the features and their availability documented
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here assume the use of the Zephyr SDK.
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When compiling a source file, the build system selects the C++ compiler based
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on the suffix (extension) of the files. Files identified with either a **cpp**
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or a **cxx** suffix are compiled using the C++ compiler. For example,
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:file:`myCplusplusApp.cpp` is compiled using C++.
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The C++ standard requires the ``main()`` function to have the return type of
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``int`` while Zephyr uses ``void`` by default. If your ``main()`` is defined in
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a C++ source file, you must select :kconfig:option:`CONFIG_CPP_MAIN` in the
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application configuration file so that Zephyr uses ``int main(void)`` instead
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of ``void main(void)``.
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.. note::
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Do not use C++ for kernel, driver, or system initialization code.
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Language Features
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*****************
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Zephyr currently provides only a subset of C++ functionality. The following
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features are *not* supported:
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* Static global object destruction
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* OS-specific C++ standard library classes (e.g. ``std::thread``,
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``std::mutex``)
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While not an exhaustive list, support for the following functionality is
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included:
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* Inheritance
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* Virtual functions
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* Virtual tables
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* Static global object constructors
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* Dynamic object management with the **new** and **delete** operators
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* Exceptions
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* :abbr:`RTTI (runtime type information)`
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* Standard Template Library (STL)
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Static global object constructors are initialized after the drivers are
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initialized but before the application :c:func:`main()` function. Therefore,
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use of C++ is restricted to application code.
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In order to make use of the C++ exceptions, the
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:kconfig:option:`CONFIG_EXCEPTIONS` must be selected in the application
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configuration file.
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Zephyr Minimal C++ Library
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**************************
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Zephyr minimal C++ library (:file:`lib/cpp/minimal`) provides a minimal subset
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of the C++ standard library and application binary interface (ABI) functions to
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enable basic C++ language support. This includes:
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* ``new`` and ``delete`` operators
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* virtual function stub and vtables
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* static global initializers for global constructors
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The scope of the minimal C++ library is strictly limited to providing the basic
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C++ language support, and it does not implement any `Standard Template Library
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(STL)`_ classes and functions. For this reason, it is only suitable for use in
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the applications that implement their own (non-standard) class library and do
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rely on the Standard Template Library (STL) components.
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Any application that makes use of the Standard Template Library (STL)
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components, such as ``std::string`` and ``std::vector``, must enable the C++
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standard library support.
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C++ Standard Library
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********************
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The `C++ Standard Library`_ is a collection of classes and functions that are
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part of the ISO C++ standard (``std`` namespace).
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Zephyr does not include any C++ standard library implementation in source code
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form. Instead, it allows configuring the build system to link against the
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pre-built C++ standard library included in the C++ compiler toolchain.
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For instance, when building with the :ref:`toolchain_zephyr_sdk`, the build
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system can be configured to link against the GNU C++ Standard Library
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(``libstdc++.a``) included in the Zephyr SDK, which is a fully featured C++
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standard library that provides all features required by the ISO C++ standard
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including the Standard Template Library (STL).
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To enable C++ standard library, select the
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:kconfig:option:`CONFIG_LIB_CPLUSPLUS` in the application configuration file.
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.. _`C++ Standard Library`: https://en.wikipedia.org/wiki/C%2B%2B_Standard_Library
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.. _`Standard Template Library (STL)`: https://en.wikipedia.org/wiki/Standard_Template_Library
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