C Union

Like structure, Union in c language is a user-defined data type that is used to store the different type of elements.

At once, only one member of the union can occupy the memory. In other words, we can say that the size of the union in any instance is equal to the size of its largest element.

Advantage of union over structure
It occupies less memory because it occupies the size of the largest member only.


Disadvantage of union over structure
Only the last entered data can be stored in the union. It overwrites the data previously stored in the union.

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

union union_name   
{  
    data_type member1;  
    data_type member2;  
    .  
    .  
    data_type memeberN;  
};  
Let's see the example to define union for an employee in c.

union employee  
{   int id;  
    char name[50];  
    float salary;  
};  


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

#include <stdio.h>  
#include <string.h>  
union employee    
{   int id;    
    char name[50];    
}e1;  //declaring e1 variable for union  
int main( )  
{  
   //store first employee information  
   e1.id=101;  
   strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array  
   //printing first employee information  
   printf( "employee 1 id : %d\n", e1.id);  
   printf( "employee 1 name : %s\n", e1.name);  
   return 0;  
}  
Output:

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.