struct in class

Question

I have struct in class and not know how to call variables from struct  please help       include  lt iostream gt  using namespace std   class E   public       struct X               int v             int main     E object  object v 10    not work   return 0

User · Answer

If you give the struct no name it will work  class E   public       struct               int v              Otherwise write X x and write e x v

User · Answer

You should define the struct out of the class like this    include  lt iostream gt  using namespace std  struct X           int v     class E   public         X var      int main     E object  object var v 10    return 0

User · Answer

It s not clear what you re actually trying to achieve  but here are two alternatives   class E   public      struct X               int v                 1   a  Instantiate an  X  within  E       X x      int main            1   b  Modify the  x  within an  E       E e      e x v   9          2  Instantiate an  X  outside  E       E  X x      x v   10

User · Answer

I declared class B inside class A  how do I access it  Just because you declare your struct B inside class A does not mean that an instance of class A automatically has the properties of struct B as members  nor does it mean that it automatically has an instance of struct B as a member  There is no true relation between the two classes  A and B   besides scoping   struct A      struct B        int v            B inner object      int main  int argc  char  argv        A object      object inner object v   123

User · Answer

Your E class doesn t have a member of type struct X  you ve just defined a nested struct X in there  i e  you ve defined a new type    Try    include  lt iostream gt   class E       public       struct X   int v         X x     an instance of  struct X      int main         E object      object x v   1       return 0

User · Answer

I d like to add another use case for an internal struct class and its usability  An inner struct is often used to declare a data only member of a class that packs together relevant information and as such we can enclose it all in a struct instead of loose data members lying around  The inner struct class is but a data only compartment  ie it has no functions  except maybe constructors    include  lt iostream gt   class E          E functions   public      struct X               int v             X variables         x         E variables       int main         E e      e x v   9      std  cout  lt  lt  e x v  lt  lt    n            E e2 5       std  cout  lt  lt  e2 x v  lt  lt    n           You can instantiate an X outside E like so        E  X xOut 24         std  cout  lt  lt  xOut v  lt  lt    n          But you shouldn t want to in this scenario         X is only a data member  containing other data members         for use only inside the internal operations of E        just like the other E s data members    This practice is widely used in graphics  where the inner struct will be sent as a Constant Buffer to HLSL  But I find it neat and useful in many cases

[c++] struct in class

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