2026-04-20 (3VO): C++ Intro
===========================

From
:doc:`/trainings/material/soup/cxx/cxx03/020-data-encapsulation/index`:

* :doc:`/trainings/material/soup/cxx/cxx03/020-data-encapsulation/c`
* :doc:`/trainings/material/soup/cxx/cxx03/020-data-encapsulation/cpp-introduction`
* :doc:`/trainings/material/soup/cxx/cxx03/020-data-encapsulation/ctor-custom`
* :doc:`/trainings/material/soup/cxx/cxx03/020-data-encapsulation/ctor-default`

Spickzettel
-----------

Original C
..........

.. literalinclude:: code/2026-04-20--point-cpp/main.c
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main.c`

Constructor
...........

* Don't leave anything uninitialized
* ``this``? Currently only used to disambiguate between two versions
  of ``x``.

.. literalinclude:: code/2026-04-20--point-cpp/main-ctor.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main-ctor.cpp`

Default Constructor
...................

* People want ``point p;`` to have a defined outcome
* |longrightarrow| default constructor

.. literalinclude:: code/2026-04-20--point-cpp/main-default-ctor.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main-default-ctor.cpp`

Non ``const`` Method: ``move()``
................................

* ``move()`` *modifies* a ``point``
* *Explicit* first parameter becomes *implicit* ``this``

.. literalinclude:: code/2026-04-20--point-cpp/main-method-move.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main-method-move.cpp`

``const`` Method: ``abs()``
...........................

* Does not modify a point
* |longrightarrow| ``const`` method

.. literalinclude:: code/2026-04-20--point-cpp/main-method-abs.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main-method-abs.cpp`

Access Specifiers: ``public`` And ``private``
.............................................

**Use case**: nobody should be able to fiddle with members ``x`` and ``y``
in an uncontrolled way!

A ``class`` definition may have access specifiers:

* ``public``: members visible to outside (default for ``struct``)
* ``protected``: members visible to derived classes |longrightarrow| a
  sign of *implementation inheritance* (discouraged)
* ``private``: members only visible to other members of same class
  (default for ``class``) |longrightarrow| *access methods*
* Let's remove the explicit ``this``, btw.

.. literalinclude:: code/2026-04-20--point-cpp/main-public-private.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main-public-private.cpp`

Separate Compilation Units
..........................

* Class definition may contain method implementations
* Expanded inline when called (entire code copied to caller)
* Not space friendly for large methods
* |longrightarrow| Put into separate compilation unit *and generate a
  real call*

.. literalinclude:: code/2026-04-20--point-cpp/main-modular.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/main-modular.cpp`

.. literalinclude:: code/2026-04-20--point-cpp/point.h
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/point.h`

.. literalinclude:: code/2026-04-20--point-cpp/point.cpp
   :language: c++
   :caption: :download:`code/2026-04-20--point-cpp/point.cpp`