C Programming - SPLessons
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Unions in C

Unions in C

shape Description

Unions in C are very similar to structures. The keyword used is "union". Union is used mainly to save the memory space and to store the values dynamically. The differences between Unions in C and structure is,
  • Structure allocates memory for every member of it separately. Whereas union allocates a single shared storage space for all of its members which will be the size of its biggest data member.
  • Manipulations made on one member will not effect the other in structures. As only single member is allocated at a time in unions, manipulations done on one member will reflect on other.

shape Conceptual figure

shape Syntax

union union_name { //declarations and initializations of members; };

Accessing the union member

shape Description

The union variable can be retrieved in the same manner as in the structure. To access the union variable . dot operator is used and to get the address of union variable * is used. Unions in C are not much used when compared to structures as they does not store all the variables at a time.

Declaring a union

[c]union example { char c; int a; float b; } ex; [/c]

Initializing a union

[c] union example { char c; int a; float b; } ex; ex.c; ex.a; ex.b;[/c]

shape Example

[c] #include<stdio.h> #include<conio.h> union car { int model; float cost; char car_name; }; int main( ) { union car c; c.model = 2011; c.cost = 100000; c.car_name='i20'; clrscr(); printf("%d\n",c.model); printf("%f\n",c.cost); printf("%c\n",c.car_name); getch(); return 0; }[/c]

Summary

shape Key Points

  • Structure "struct" keyword is replaced with "union" and is used in shareable mode.
  • Unions are used to focus on memory as each member within union structure is assigned its own unique storage¬†space.

shape Programming Tips

Do not initialize multiple members using union.The compiler gives an error.