C++: Class within another class as type?

Question

could someone explain me this kind of "inheritance" which can be found in class Y: private?

class X
{
  private: char c_;
  public: X(char c) : c_(c){}
};

class Y
{
  private: X x_; // What is this ?
  public: Y(X x): x_(x){}
};

int main()
{
  X m('a');
  Y *test = new Y(m);

  delete test;
  return 0;
}

It's the same as `private: char c_;`. It's just a member variable. Sounds like you could use a [good C++ book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) — NathanOliver, Jun 15 '17 at 16:18
@NathanOliver so it is just synonym ? Has nothing to do with properties from class X ? — Ryad Kovach, Jun 15 '17 at 16:21
No it is not a synonym. It declares a class member named `x` that has the type of `X`. Just like `private: char c_;` declared a class member named `c` of type `char`. — NathanOliver, Jun 15 '17 at 16:22
https://stackoverflow.com/questions/1711990/what-is-this-weird-colon-member-syntax-in-the-constructor — TallChuck, Jun 15 '17 at 16:23

score 1 · Answer 1 · answered Jun 15 '17 at 17:59

1

This is not inheritance, as Y does not derive from X.

This is just simple encapsulation. X x is just a member variable of Y, no different than char c_ being a member variable of X.

answered Jun 15 '17 at 17:59

Remy Lebeau

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So, it has nothing to do with the `class X` above ? Member variable of type `X` is saved as number(`int,double`) or as a `char` ? – Ryad Kovach Jun 16 '17 at 15:16
@RyadKovach I don't understand what you are asking. – Remy Lebeau Jun 16 '17 at 15:26
@RemyLebau Just wanna make sure, that `class Y` has nothing to do with `class X` ? – Ryad Kovach Jun 16 '17 at 22:35
@RyadKovach: `class X` is independent of `class Y`. `class Y` has a member that is of type `X`, so it depends on `class X`, but is not derived from it. – Remy Lebeau Jun 16 '17 at 22:40

C++: Class within another class as type?

1 Answers1