A union is a special data type available in C that allows to store different data types in the same memory location just like structures in C.

Union uses a single shared memory location which is equal to the size of its largest data member. It provide an efficient way of using the same memory location for multiple-purpose.

Union is used to store student information, employee information, product information, book information etc.

Defining a Union

The union keyword is used to define union. syntax to define union in c is:

union [union tag] {
   member definition;
   member definition;
   ...
   member definition;
} [one or more union variables]; 

The following example displays the total memory size occupied by the above union:-

 #include <stdio.h>
    #include <string.h>

    union Data {
       int i;
       float f;
       char str[20];
    };

    int main( ) 
    {

       union Data data;        

       printf( "Memory size occupied by data : %d\n", sizeof(data));

       return 0;
    }

Output:- When the above code is compiled and executed, it produces the following result -

 Memory size occupied by data : 20