Union
A union is a special data type available in C that allows to store different data types in the same memory location. You can define a union with many members, but only one member can contain a value at any given time. Unions provide an efficient way of using the same memory location for multiple-purpose.
Defining a Union
To define a union, you must use the keyword “union”.
union student
{
int roll;
char name[20];
float per;
};
| Structures | Union |
| Keyword “struct” is used to declare a structure | Keyword “union” is used to declare a union |
| struct student1 { int roll; char name[20]; float age; }; |
union student2 { int roll; char name[20]; float age; }; |
| Structure variables are declared as Struct student1 s1; |
Union variables are declared as Union student2 s2; |
| Data elements of a structure are accessed using the dot(.) operator Example: Struct student1 s1; Scanf(“%d”,&s1.roll); Scanf(“%s”,s1.name); Scanf(“%f”,&s1.age); |
Data elements of a union are accessed using the dot(.) operator Example: union student2 s2; Scanf(“%d”,&s2.roll); Scanf(“%s”,s2.name); Scanf(“%f”,&s2.age); |
|
Size of a structure / structure variable is equal to the sum of the size of all data elements Note:in codeblocks size will be 28 as size of int is taken as 4 bytes |
Size of a union / union variable is equal to the size of the largest data elements.
|
| In case of structure all the data elements can be used at any point of time as they occupy different memory locations. |
In case of union only one data element can be used at any point of time as they share memory locations. |
|
The data elements of a structure occupy separate memory location roll: 2 bytes |
The data elements of a union share the same memory location roll,name,age: 20 bytes |
|
Structure occupies more memory |
Union occupies less memory |
|
Structure is used when all the data elements are required at the same time. |
Union is used when only one data element is required at a time. |
