C Union

Union is similar to the structures, it also contains number of members like structures. In C, union is identified by the keyword union The members of union share the same memory location within the computer, whereas each structure member has its own memory location within the computer. At any time of compilation, only one member of the union can reside in that memory location. The union require bytes that are equal to the bytes required by largest member within union. The union allocates fixed bytes. Thus, unions are used to conserve or save memory.

Declaration of Union

The declaration of union is similar to structure, except the keyword union instead of struct.

Syntax - Union

union unionname { 
data type member1;
data type member2;
}variable1, variable2;

C program - Difference Between Structure and Union

#include <stdio.h>
int main()
{
//structures declartion
struct sample{
    double d1;     //occupies 8 bytes in memory
    float f1;     //occupies 4 bytes in memory
}s1;
//Union declartion
union samp{
    double d2;     //occupies 8 bytes in memory
    float f2;     //occupies 4 bytes in memory
}u1;
printf("\nSize of Structure : %d ", sizeof(s1));
printf("\nSize of Union : %d ", sizeof(u1));
return 0;
}

Accessing a Union Member

A union member can be accessed similar to structure member, that by using (.)dot or period operator. The general format is as follows,

unionvariablename.membername;

#include <stdio.h>
int main()
{
/structures declartion
struct sample{
    int a;
    int b;
}s1;
//Union declartion
union samp{
    int c;
    int d;
}u1;
s1.a = 10;
s1.b = 20;
printf("\nThe Structure member values a and b are : %d %d ", s1. a, s1.b);
u1.c = 30;
u1.d = 40;
printf("\nThe Union member values c and d are : %d %d ", u1. c, u1.d);
return 0;
}

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