CODEWITHSUNDEEP
c++structunions
Kishore Pula
Kishore Pula

Reputation: 332

How to define and access unnamed structure inside an anonymous union?

Can anyone explain what's wrong with this implementation?

I am encountering following errors

error: a storage class on an anonymous aggregate in class scope is not allowed

error: use of deleted function ‘ResultUnion::ResultUnion()’

#include<iostream>
#include<vector>
using namespace std;
enum MediaKind { Container, Music};
typedef vector<string> StringList;
struct ResultUnion {
  enum MediaKind kind;
  static union {
    struct { 
            string Type; 
            StringList List;
            bool searchable;
            }c; 
    struct { 
            string Type;
            uint32_t duration;
            }m;
   };
};

int main()
{
ResultUnion ResultUnionobj[2];
ResultUnionobj[0].kind = Container;
ResultUnionobj[0].c.Type = "Container";
ResultUnionobj[1].kind = Music;
ResultUnionobj[1].m.Type = "Music";
cout << "first:" << ResultUnionobj[0].c.Type << endl << "second:" << ResultUnionobj[1].m.Type;
}

Upvotes: 0

Views: 148

Answers (1)

vmario
vmario

Reputation: 411

Until C++11:

Unions cannot contain a non-static data member with a non-trivial special member function (copy constructor, copy-assignment operator, or destructor).

And since C++11:

If a union contains a non-static data member with a non-trivial special member function (copy/move constructor, copy/move assignment, or destructor), that function is deleted by default in the union and needs to be defined explicitly by the programmer.

If a union contains a non-static data member with a non-trivial default constructor, the default constructor of the union is deleted by default unless a variant member of the union has a default member initializer.

(Union declaration)

In short, string in union is not a good idea.

Upvotes: 1

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