Difference between structure and union in C

What is a Union in C?

A union in C is a user-defined data type that allows storing different data types in the same memory location. Unlike structures, where each member has its own memory space, a union shares memory among its members, allowing only one member to be active at any given time. This makes unions efficient for conserving memory when different types of data need to be stored interchangeably.

Let us check how to define a union known as “student”.

union student{
char student_firstname;
char student_lastname;
int student_age;
double student_height;}

We can then use “Student newStudent” to declare the function and dot operators are also used when trying to reach different data types.

Example of Union in C 

Student newStudent; 
 newStudent.age = 15; 
 newStudent.height = 5.11;

Here is an example of using unions in C where the output gets corrupted due to the memory location being shared by all the member data types:

• C

C

#include <stdio.h>

union stats
{
    int revenue;
    float total_sales;
    char condition;
};

int main( )
{
    union stats it;
    it.revenue = 5000;
    it.total_sales = 7000;
    it.condition = 'p';
    
    printf("%d\n", it.revenue);
    printf("%f\n", it.total_sales);
    printf("%c\n", it.condition);
    
    return 0;
}

You can also try this code with Online C Compiler

Run Code

Output:

You can also read about the dynamic arrays in c, and  Tribonacci Series

Functions and Similarities Between Union and Structure in C

Difference Between Structure And Union In C

Advantages of Structure in C

• A structure can contain multiple data items with similar attributes inside the same memory location. This is especially helpful when gathering data about the same subjects with similar parameters.
• Structures are stable and easier to maintain as the entire records can be represented under a single name. This allows us to pass functions with complete sets of records using single parameters.
• Arrays of structures can be used to effectively incorporate more records with similar data types.

Advantages of Union in C

• Unions are popular for occupying less memory.
• Unions are helpful when storing the data of a single data member. And, unions are especially useful for storing multiple data members in the same memory location.

Drawbacks Of Structure Vs Union In C

Structures and unions both have their own set of drawbacks. Using unions sometimes can cause massive errors in functions due to the nature of combining every single member when passing a function.

Meanwhile, structures pose a problem for scalability and they become harder to manage when projects become complex, requiring much more storage as well.

Let us learn the different disadvantages that we face when working with each one of them.

Structures

• Changes in any data structure require changes at multiple other places in the code. This makes it more time-consuming to use and harder to track.
• Structures are slower and require dedicated memory for all their data.

Unions

• Members cannot be processed with varying values simultaneously. Users are limited to using a single member.
• Unions assign a single memory location for their members, thus causing complexities, cluttering and many other errors when working with varying data types. All of this is due to not having dedicated memory allocations.

Frequently Asked Questions

What is structure and union in C?

Unions and structures are user-defined data types that can be used for combining multiple data items with various attributes and passing functions through incorporating these data items.

Which is better, union or structure?

Structures are more suitable for reliable and consistent performance when working with multiple data types. However, unions are less memory-intensive and are more effective when working with a massive number of members or objects.
Structures are convenient but not made for large projects. Structure and union differences in c can be easily noticed when working with different data types possessing various attributes or when there are a huge number of data items.

Why is union used in C?

Unions are used in C to define functions for multiple data items, which are of different data types. Unions are highly used especially when data types are unknown.

What are the two types of unions?

The two types of unions are tagged and untagged unions. Tagged unions are capable of handling variable but fixed data types. Meanwhile, untagged unions are used when not wanting to allocate space for storing the data type tag.

What is the relationship between structures and arrays?

Like there are arrays of other data types, there can be arrays of structures as well. Similarly, structures can contain arrays as well. Structures and arrays can also be used together to create a nested representation when dealing with arbitrary levels of complexity.

Conclusion

Both structures and unions offer their own set of benefits and disadvantages. It really comes down to a matter of preference and the scale of the program (or project) when deciding if one should use structures or unions. While structures are more adaptive, versatile, and capable of accessing multiple objects parallelly, unions are much more portable and easy to debug.

Deciding which data type to use in C depends on the type of data items that will be used and how they are related to each other. Unions are the best when using data types that are unknown, while structures are best for working with objects (data) with different attributes.

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