UNION in C programming

Union follow the same syntax as structure with a major difference in terms of storage. In structure every structure elements has their own storage location, whereas in union all the members share the same location. So in a union there may be a number of elements but only one member can be used at a time. The declaration syntax of union is as follows

union  tag

{

 int i;

float b;

char c;

}var;

Here the variable var is of type union tag. Here the union contains three data members of different types but we can use only one member at a time. This is due to the fact that only one location is provided to the union variable. Here the member float b will take the maximum space (4 bytes), so the space provided for the union variable is 4 bytes. If the above declaration were a structure then the space required for the variable would have been 7 bytes.

Like structure members, we can access union members with statements like var.i, var.b, var.c. While accessing value from an union member, we should make sure that we are accessing the member in which the last value is assigned.

Difference between structure and union

In a structure in C programming language, each member has a storage location once it is associated with the structure. In a union, all the members use the same location. A union can contain members of different data types, but it can handle only one member at a time

The storage location allocated to a structure is the sum total of the storage location needed to store all the members of the structure. In a union, the storage size is equal to the size of the largest member of the union.