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C Union

Like structure, Union in c language is a user defined datatype that is used to hold different type of elements.

But it doesn’t occupy sum of all members size. It occupies the memory of largest member only. It shares memory of largest member.


Advantage of union over structure

It occupies less memory because it occupies the memory of largest member only.

Disadvantage of union over structure

It can store data in one member only.

Defining union

The union keyword is used to define union. Let’s see the syntax to define union in c.

  1. union union_name
  2. {
  3.     data_type member1;
  4.     data_type member2;
  5.     .
  6.     .
  7.     data_type memeberN;
  8. };

Let’s see the example to define union for employee in c.

  1. union employee
  2. {   int id;
  3.     char name[50];
  4.     float salary;
  5. };

C Union example

Let’s see a simple example of union in C language.

  1. #include <stdio.h>
  2. #include <string.h>
  3. union employee
  4. {   int id;
  5.     char name[50];
  6. }e1;  //declaring e1 variable for union
  7. int main( )
  8. {
  9.    //store first employee information
  11.    strcpy(, “Sonoo Jaiswal”);//copying string into char array
  12.    //printing first employee information
  13.    printf( “employee 1 id : %d\n”,;
  14.    printf( “employee 1 name : %s\n”,;
  15.    return 0;
  16. }


employee 1 id : 1869508435
employee 1 name : Sonoo Jaiswal

As you can see, id gets garbage value because name has large memory size. So only name will have actual value.