Introduction to Union in C Language

It looks same as structure but implementation is different. Difference between structure and union is that the members of structure get different memory locations but members of a union share common memory location.

C Language Compiler allocates memory to hold that element of union which has the largest size.

Syntax

union <uname>

{

<Data-type1> var1;

<Data-type2> var2;

:

};

uname is the name of union specified by programmer.

Data-type1, Data-type2,…  are data types of elements of union.

var1, var2,… are members  of union.

Union variable

We can declare variables of a union just like structure.

Syntax:

union <tag_name> var1,var2,…..varN;

Here, tag_name is the name of union of which we want to declare variables.

var1,var2,……..varN are names of union variables.

Program to demonstrate union.

#include<stdio.h> union demo { int a; float b; }; int main() { union demo d1; printf(“%d”,sizeof(d1)); d1.a=13; d1.b=5.5; printf(“\nd.a=%d”,d.a); printf(“\nd.b=%f”,d.b); return(0); }

Output

Size of union variable d=4 d.a=13137 d.b=4.600000

Description

Size of d1 is displayed 4 because the size of largest element of union i.e. b(float type) is 4 bytes.  The value of 1d.b is displayed correctly because union variable can hold value of only one of its elements at a time. The latest value stored is of d.b.

Lesson tags: declare union variable in c, difference between structure and union, program to use union in c, size of a union variable in c, union in c

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