Union
Union is just similar to structure it is also used to create user define datatype. Like structures, unions are also a group of a number of variables. However, member variables do not have separate spaces allocated for them.
A single space in the memory corresponding to the largest member variable is assigned to a union. As a result a union type data stores a single value which can be accessed by referencing individual members of the union.
Interpretation of the value stored in a union depends on the variable which is used to access the stored value. Union type data are particularly useful when space in the memory is at premium.
Syntax:
union
{
data_type_1 variable_name_1;
data_type_2 variable_name_2;
…
data_type_n variable_name_n;
};
Example
union abc
{
int a1;
char a2;
float a3;
};
union abc union1;
WAP to compare memory on struct and union
#include<stdio.h>
#include<conio.h>
main(){
struct stag
{
char c;
int i;
float f;
};
union utag
{
char c;
int i;
float f;
};
union utag uvar;
struct stag svar;
clrscr();
printf("size of svar = %u ",sizeof(svar));
printf("address of svar = %u",&svar);
printf("address of member : %u %u %u",&svar.c,&svar.i,&svar.f);
printf("size of uvar = %u ",sizeof(uvar));
printf("address of uvar = %u",&uvar);
printf("address of member : %u %u %u",&uvar.c,&uvar.i,&uvar.f);
getch();
}
Output
size of svar = 7
address of svar = 65514
address of member = 65514 65515 65517
size of uvar = 4
address of uvar 65522
address of member = 65522 65522 65522