An anonymous union.
#include <iostream>
#include <cstring>
using namespace std;
int main()
{
// define anonymous union
union {
long l;
double d;
char s[4];
} ;
// now, reference union elements directly
l = 100000;
cout << l << " ";
d = 123.2342;
cout << d << " ";
strcpy(s, "hi");
cout << s;
return 0;
}100000 123.234 hi
An example of a union
#include <iostream>
using std::cout;
using std::endl;
union Number
{
int integer1;
double double1;
};
int main()
{
Number value;
value.integer1 = 100;
cout << value.integer1 << "\ndouble: " << value.double1
<< endl;
value.double1 = 100.0;
cout << value.integer1 << "\ndouble: " << value.double1
<< endl;
return 0;
}100
double: 4.24399e-314
0
double: 100
A union is created with several data types.
#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);
}A union with method
#include <iostream>
using namespace std;
union u_type {
u_type(short int a) { i = a; };
u_type(char x, char y) { ch[0] = x; ch[1] = y; }
void showchars(){
cout << ch[0] << " ";
cout << ch[1] << "\n";
}
short int i;
char ch[2];
};
int main()
{
u_type u(1000);
u_type u2("X", "Y");
cout << "u as integer: ";
cout << u.i << "\n";
cout << "u as chars: ";
u.showchars();
cout << "u2 as integer: ";
cout << u2.i << "\n";
cout << "u2 as chars: ";
u2.showchars();
return 0;
}u as integer: 1000
u as chars: F ?
u2 as integer: 22872
u2 as chars: X Y
Put int and float into a union
#include <iostream>
using namespace std;
int main(void){
union
{
int my_data;
float his_data;
};
my_data = 3;
cout << "Value of my_data is " << my_data;
his_data = 1.2345;
cout << "\nValue of his_data is " << his_data;
}Unions and Classes Are Related
#include <iostream>
using namespace std;
union swap_byte {
void swap();
void set_byte(unsigned short i);
void show_word();
unsigned short u;
unsigned char c[2];
};
void swap_byte::swap()
{
unsigned char t;
t = c[0];
c[0] = c[1];
c[1] = t;
}
void swap_byte::show_word()
{
cout << u;
}
void swap_byte::set_byte(unsigned short i)
{
u = i;
}
int main()
{
swap_byte b;
b.set_byte(49034);
b.swap();
b.show_word();
return 0;
}Using an anonymous union: members integer1, double1 and charPtr share the same space
#include <iostream>
using std::cout;
using std::endl;
int main()
{
union
{
int integer1;
double double1;
char *charPtr;
};
integer1 = 2;
cout << integer1 << endl;
double1 = 4.4;
cout << double1 << endl;
charPtr = "union";
cout << charPtr << endl;
return 0;
}2
4.4
union
