Defining a Union

Introduction Generations of Computers Classification of Computers Basic Anatomy of a Computer System Memory Management Computer Software Operating System

Algorithm Flowcharts

Programming Language Generations of Programming Languages Introduction to C Structure of C Programming Language Integrated Development Environment First C program, Hello World Executing a C Program Constants in C Variables in C C Storage Classes and Storage Class Specifiers

Introduction Arithmetic operators Relational Operators Logical Operators Assignment Operator Increment and Decrement Operators Conditional Operators Bitwise Operators Precedence and Associativity

Control Instructions in C if Statement in C if-else Statement Nested if-else statement else if ladder Switch Statements in C

Loops Introduction for Loop while loop in C do-while Loop break and continue statements

Array in C One Dimensional array Two Dimensional Array Multidimensional Arrays

Modular Programming Functions

Searching Techniques Linear Search Algorithm Binary-Search-Algorithm

Sorting Introduction Bubble Sort

What is Strings Standard Library String Functions

Structure Introduction Defining a Structure Declaration of Structure Example of Structure Union Introduction Defining a Union Accessing Union Members

Pointers in C Accessing the Address of a variable Pointer Operations

Dynamic Memory Allocation

To define a union, you must use the union statement in the same way as you did while defining a structure. The union statement defines a new data type with more than one member for your program. The format of the union statement is as follows −

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

The union tag is optional and each member definition is a normal variable definition, such as int i; or float f; or any other valid variable definition. At the end of the union's definition, before the final semicolon, you can specify one or more union variables but it is optional. Here is the way you would define a union type named Data having three members i, f, and str –

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

Now, a variable of Data type can store an integer, a floating-point number, or a string of characters. It means a single variable, i.e., same memory location, can be used to store multiple types of data. You can use any built-in or user-defined data types inside a union based on your requirement.

The memory occupied by a union will be large enough to hold the largest member of the union. For example, in the above example, Data type will occupy 20 bytes of memory space because this is the maximum space that can be occupied by a character string.

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

#include <stdio.h>
#incldue<conio.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));
getch ();
 return 0;
}

Output:

Memory size occupied by data : 20

Fundamentals of the Computer System

Introduction to Algorithm

Programming Basics

Operators in C

Conditional Branching

Iteration and Loops

Array in C

Functions in C

Searching Algorithms

Sorting Algorithms

Strings

Structures and Union

Pointers in C

File Handling in C

Advanced

Defining a Union

Output: