What Is Union Data Type in C Programming?

What Is Union Data Type in C Programming?

In C programming, a union is a user-defined data type that allows different data types to be stored in the same memory location. It is similar to a structure, but with one key difference – whereas a structure allocates memory for each member variable separately, a union allocates memory for only one member variable at a time.

Declaration and Syntax:

The syntax for declaring a union in C programming is as follows:

union union_name {
    data_type1 member_name1;
    data_type2 member_name2;
    .
    .
};

The keyword union is used to declare the union, followed by the union_name. Inside the curly braces, you can define multiple members with their respective data types.

Accessing Union Members:

You can access the members of a union using the dot (.) operator. However, since only one member can have a value at any given time, it is important to access the correct member.

// Define and initialize a union
union myUnion {
    int num;
    float decimal;
};

// Accessing union members
int main() {
    union myUnion u;
    
    u.num = 10; // Accessing integer member
    printf("Number: %d\n", u.num);
    
    u.decimal = 3.14; // Accessing float member
    printf("Decimal: %.2f\n", u.decimal);
    
    return 0;
}

#include <stdio.h>

// Define a union
union myUnion {
    int num;
    float decimal;
};

int main() {
    printf("Size of union: %lu bytes\n", sizeof(union myUnion));
    
    return 0;
}