Explain the pointers to unions in C language

CServer Side ProgrammingProgramming

A union is a memory location that is shared by several variables of different data types.

Syntax

The syntax for the pointers to unions in C programming is as follows −

union uniontag{
   datatype member 1;
   datatype member 2;
   ----
   ----
   datatype member n;
};

Example

The following example shows the usage of union of structure.

union sample{
   int a;
   float b;
   char c;
};

Declaration of union variable

Following is the declaration for union variable. It is of three types as follows −

Type 1

union sample{
   int a;
   float b;
   char c;
}s;

Type 2

union{
   int a;
   float b;
   char c;
}s;

Type 3

union sample{
   int a;
   float b;
   char c;
};
union sample s;
  • When union is declared, the compiler automatically creates largest size variable type to hold variables in the union.

  • At any time only one variable can be referred.

  • Same syntax of structure is used to access a union member.

  • The dot operator is for accessing members.

  • The arrow operator ( ->) is used for accessing the members using pointer.

We have pointers to unions and can access members using the arrow operator (->) just like structures.

Example

The following program shows the usage of pointers to union in C programming −

 Live Demo

#include <stdio.h>
union pointer {
   int num;
   char a;
};
int main(){
   union pointer p1;
   p1.num = 75;
   // p2 is a pointer to union p1
   union pointer* p2 = &p1;
   // Accessing union members using pointer
   printf("%d %c", p2->num, p2->a);
   return 0;
}

Output

When the above program is executed, it produces the following result −

75 K

Example 2

Consider the same example with different input.

 Live Demo

#include <stdio.h>
union pointer {
   int num;
   char a;
};
int main(){
   union pointer p1;
   p1.num = 90;
   // p2 is a pointer to union p1
   union pointer* p2 = &p1;
   // Accessing union members using pointer
   printf("%d %c", p2->num, p2->a);
   return 0;
}

Output

When the above program is executed, it produces the following result −

90 Z
raja
Published on 12-Mar-2021 06:16:18
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