A union is created with several data types. : union « Data Types « C++ Tutorial

1. C++ Tutorial
2. Data Types
3. union

#include <iostream.h>

union unmany_types {
 char c;
 int ivalue;
 double fvalue;
 double dvalue;
} unmy_union;
  
int main(void)
{
 unmy_union.c='b';
 cout << unmy_union.c << "\n";

 unmy_union.ivalue=1990;
 cout << unmy_union.ivalue << "\n";

 unmy_union.fvalue=19.90;
 cout << unmy_union.fvalue << "\n";

 unmy_union.dvalue=987654.32E+13;
 cout << unmy_union.dvalue << "\n";

 // invalid I/O
  
 cout << unmy_union.c << "\n";
 cout << unmy_union.ivalue << "\n";
 cout << unmy_union.fvalue << "\n";
 cout << unmy_union.dvalue << "\n";

 // union size
 cout << "The size of this union is: " << sizeof(unmany_types) << " bytes." << "\n";

 return (0);
}