Difference Between Structure and Union

Difference Between Structure and Union in C

Structure and Union Difference

The Key Difference Between Structure and Union is that Both the structure and union are user-defined data types in C Language. Structure is a collection of logically related data items of different data types grouped together under a single name. Union is a user-defined data type just like structure.

Comparison Chart

Structure Union
Keyword struct defines a structure Keyword union defines a union.
Each member is assigned its own unique storage area. All members share the same storage area.
Total memory required by all members is allocated. Maximum memory required by the member is allocated.
All members are active at a time. Only one member is active time.
All members can be initialized. Only the first member can be initialized.
It requires more memory. It requires less memory.
No Anonymous feature. Anonymous union can be declared.
Example:

struct SS
{
int a;
float b;
char c;
};

1 byte for c
2 byte for a
4 byte for b
Total bytes = 1 + 2 + 4 = 7 bytes.

Example:

union UU
{
int a;
float b;
char c;
};

4 bytes for c,b,a

Structure

  • Structure is a collection of logically related data items of different data types grouped together under a single name.
  • Structure is a user-defined data type.
  • Structure helps to organize complex data in a more meaningful way.

Syntax of Structure

struct structure_name
{
data_type member1; 
data_type member2;
………….
};
  • struct is a keyword.
  • structure_name is the tag name of a structure.
  • member1, member2 are members of a structure.

Example

#include<stdio.h>
#include<Conio.h> 
struct book
{
char title[100]; 
char author[50];
int pages; 
float price;
};
void main()
{
struct book book1;
printf("enter title, author name, pages and price of book"); 
scanf(“%s”,book1.title);
scanf(“%s”, book1.author); 
scanf("%d",&book1.pages); 
scanf("%f",&book1.price); 
printf("\n detail of the book"); 
printf(“%s”,book1.title); 
printf(“%s”,book1.author);
printf("%d",book1.pages);
printf("%f",book1.price); 
getch();
}
  • book is a structure whose members are title, author, pages, and price.
  • book1 is a structure variable.

Union

  • Union is user-defined data type just like structure.
  • Each member in structure is assigned its own unique storage area whereas, in Union, all the members share a common storage area.
  • All members share the common area so only one member can be active at a time.
  • Unions are used when all the members are not assigned value at the same time.

Example

union book
{
char title[100]; 
char author[50];
int pages; 
float price;
};

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