Accessing string in a union inside a struct in C++14 - c++11

Question

Can anyone please explain how to use and access string in a union inside a structure with the help of unrestricted union?
#include <iostream>
#include <string>
using namespace std;
typedef struct {
int height;
int width;
} Page;
typedef struct {
int test;
union {
Page page;
int intVar;
string stringVar;
} VarUnion;
} VariableDataStruct;
int main()
{
VariableDataStruct structeg;
structeg.VarUnion.stringVar = "Hello";
return 0;
}
Currently getting following errors on compilation:
unionstring2.cc: In function ‘int main()’:
unionstring2.cc:22:24: error: use of deleted function ‘VariableDataStruct::VariableDataStruct()’
VariableDataStruct structeg;
^
unionstring2.cc:11:16: note: ‘VariableDataStruct::VariableDataStruct()’ is implicitly deleted because the default definition would be ill-formed:
typedef struct {
^
unionstring2.cc:11:16: error: use of deleted function ‘VariableDataStruct::::()’
unionstring2.cc:13:19: note: ‘VariableDataStruct::::()’ is implicitly deleted because the default definition would be ill-formed:
union {
^
unionstring2.cc:16:11: error: union member ‘VariableDataStruct::::stringVar’ with non-trivial ‘std::basic_string<_CharT, _Traits, _Alloc>::basic_string() [with _CharT = char; _Traits = std::char_traits; _Alloc = std::allocator]’
string stringVar;
^
unionstring2.cc:11:16: error: use of deleted function ‘VariableDataStruct::::~()’
typedef struct {
^
unionstring2.cc:13:19: note: ‘VariableDataStruct::::~()’ is implicitly deleted because the default definition would be ill-formed:
union {
^
unionstring2.cc:16:11: error: union member ‘VariableDataStruct::::stringVar’ with non-trivial ‘std::basic_string<_CharT, _Traits, _Alloc>::~basic_string() [with _CharT = char; _Traits = std::char_traits; _Alloc = std::allocator]’
string stringVar;
^
unionstring2.cc:22:24: error: use of deleted function ‘VariableDataStruct::~VariableDataStruct()’
VariableDataStruct structeg;
^
unionstring2.cc:18:11: note: ‘VariableDataStruct::~VariableDataStruct()’ is implicitly deleted because the default definition would be ill-formed:
} VariableDataStruct;
^
unionstring2.cc:18:11: error: use of deleted function ‘VariableDataStruct::::~()’

Answer 1

The error you're getting is not about accessing union, it's about not being able to instantiate your struct:
error: use of deleted function ‘VariableDataStruct::VariableDataStruct()’
You need to provide a constructor for your struct that sensibly initializes the union.

Answer 2

Unions with members with non-trivial special member functions (constructor, assignment, destructors) (such as std::string) must define these special functions as well. Since this union does not provide the designation which member is currently in use, those special member functions cannot be defined.
Use std::variant<Page, int, std::string> instead.